(One) “On the leash she will charge other dogs, barking and growling with her hair up on her back." (Two) “She gets really amped up when it’s the both of us. She gets much more fearful and barks more when it’s the both of us together. She will lunge at another dog and I have to hold her back.”
On this forum I've noticed you can barely mention the word “pack” because people go bananas remembering a particular celebrity trainer’s (negative) use of the “theory of dominance” and punitive action! This is (instead) about incentivizing and rewarding! But the suggestion will also not be a quick fix. Know that when she is off leash with dogs of equal temperament she is comfortable enough not to be aggressive, not having a need to demonstrate confidence versus insecurity (which means "rank").
Your statements (one) & (two) shows the same basic attitude/reactivity, just to a matter of differing degree. Know that you are the most important element in your dog’s life (you supply food, exercise and protection). Therefore you are her “resource” (sorry, it’s not just about love) and it means that she is protecting (or valuing) what you mean to her. With your husband she is that much stronger with two, than you alone. Which gives her more confidence to ward off (or warn) intruders into her space when you are together. With the addition of your husband, the group increases and she is further emboldened. Her group has now become even more formidable for whatever she encounters on the street. Regarding her personality, as a dog (on leash) she has no requirement to mingle, even though you might wish to be “friendly” with others.
While this won't be a quick fix, it's a good investment of time for all things going forward! Training takes time and consistency because it’s actually about “shaping” behavior incrementally. Corrections only tell a dog there's a penalty for what they've (just) done. To some degree a dog “seems” to react, but that's only because there’s a change in your voice/scent and body language. However they can’t build a constructive pattern (solution) to avoid the correction (without a demonstration from you). Corrections can seem to work through intimidation, which makes an insecure/sensitive dog avoid discomfort by shutting down. However an overly confident dog will continue to test the situation until such a road-block occurs that it devalues the attempt. And the payoff is no longer worth it. Unfortunately some dogs never submit.
The first thing a dog has to learn is engagement and focus with you. This is really, really tough to teach when not learned from a young age. The goal is to make you more important and exciting (rewarding) in your dog’s life than anything else she can imagine! To that purpose, you are going to manage all her pleasures. This is going to take time. Lots of time. So build the relationship inside the house at first. Maybe don’t go for a walk for awhile until you fix this relationship. You can do it as described below:
Marker trainer doesn't mean you need a "clicker" but does mean the immediate (positive) stimulus a dog gets in return for a behavior. Dogs ALWAYS, always act for a payoff. And in your dog's world remember that you represent safety, protection, confidence and security. That’s her “pack” (group or family). And her instinctive loyalty is to you for all those reasons. To teach engagement and focus, you must capture her attention! First you have to “charge” the mark (meaning to promise the payoff). Start simply, by teaching “come” (she does) and instantaneously give a treat! And I mean instantaneously. If she comes and sits (all in one move) treat that combo behavior! And only reinforce that combo behavior. Don't confuse between the two (a come with no sit). Never verbally correct, either ignore a failed behavior or reward it. Pick a HIGH value treat, and you may feed a portion of her meal. Do this 20 times in a row. When she comes/sits, treat. Ideally you want her eyes to meet yours, which is called focus! Eye contact is meaningful in the dog’s world. You want it to be a positive link! "Come/sit/eye focus" ...one treat. Spread the training randomly throughout the day. So she learns that every single time she comes/sits/eye contact, she gets a treat! Super yummy treat! Wow, she is going to be at your heels (if she really likes food) all day long.
Eventually you can shape her behavior, not only to come/sit, but to slide over to your side. You might have to nudge her side gently to lean against your leg. She might start accidentally offering that behavior. So build on it! To make it one smooth action, come/sit/eye/at your side. When she snuggles up against your leg, then that’s a huge reward (jackpot means double treat, happy voice!!). And you can gradually change your “come” word to “side” (come/sit/eye/side .... in a waiting position). You'll create a release word "done" which lets her return to whatever she's been doing! Always, always release her when you're done or interrupted.
Next you build in duration, come/sit/eye/at your side (one, two, three beats) treat. Repeat 20 times, as you add a beat. Build up the duration, so she’s learned to WAIT for her reward! Do this for about a week. (You're teaching & establishing trust). When that behavior is met, teach come/sit/eye/side … then walk 2 steps with you. Build up the distance (which is duration) …. 5 steps, 10 steps. You're trying to teach her to be "glued" to your side. When you stop for the final time (training session) and your last treat, don't forget to release. So that what you’re really teaching is the value of focusing on you, walking at your side, and paying attention to your directions … to earn a reward! And to be rewarded with praise and happy talk! Which will all eventually lessen her anxiety out on the walk.
Once that behavior is nailed, teach during distractions. In your yard. She may have to be a little more hungry just to ensure her attention. To teach that you are a more important person than outside noises, smells, squirrels, cars, people (whatever). You can make the exercises even more fun, by alternating the routine with a little playtime (like running in the opposite direction). Or working in some playtime with a special tug toy (reserved only for training time). Or whatever makes her most interested in interacting with you! Use a happy, enthusiastic voice, which is confidence building, and spending all that attention on her. Positive training ... is bonding with your dog!!
Because - this is key …
You’re going to want to take this “reward system” on the road with you!! You spot a potential distraction up ahead, you engage your dog, and expect her to focus on you. Ideally to sit at your side. When she does ... treat. If you’ve built in duration, you can solicit her patience as you walk a few steps (then treat), repeat. And eventually, if you’ve transitioned well enough, (hopefully) can offer that “tug toy” to distract her from her distraction, because you’re offering her fun time!!! Which means, you’re also replacing her previous feeling of anxiety (which was that threatening, stress producing situation) into a particularly fun, playful, REWARDING, happy interaction with you! Now she’s become a “good” dog for positive behavior (and you’ve eliminated corrections) which had been turning the walk into a struggle for both of you.
Later on introduce the word “heel, go, proceed, forward” (whatever) meaning the cue for her to move forward with you, at your side, when you’re ready to walk ahead! Make sure she's keeping an eye on you, because training is an ever ongoing work in process!