Biting Pomeranian

For the first issue, I would question whether this dog is actually suddenly becoming aggressive. It's probably more like this: The dog is so excited that it wants to take out it's excited energy on something. (This is the most likely cause.) Since biting/chewing is calming to dogs and is fun, he decides to bite something, and that just happens to be this person's partner. In this case, the owner should make sure the dog has calmed down before going for a shower, should make sure the dog has had enough exercise an mental stimulation, and the partner should try to redirect the dog to a toy or chew.
For the second: The dog seems to be scared by the owner putting on the lead, and is therefore defending itself. The owner should make sure they aren't leaning over the dog when attaching the lead, as this can seem threatening. This is one of the most common causes for this issue, especially in small dogs. They should also make sure the collar/harness and leash are comfortable. If the dog is scared of the leash itself, they could try slowly getting the dog used to having the leash around before trying to attach it. They should be sure not to suddenly and quickly approach the dog and clip the lead on. They should make sure the dog sees them coming with the leash, and is prepared for them to clip the lead on. If the leash is on a choke chain, then, regardless of anything else, that choke chain needs to go away, they're dangerous and potentially deadly. If the leash is on some other aversive tool, like a front-clip harness, head halter, or prong collar, or if they use the leash to give corrections or "leash pops", they should stop. The dog is not responding well to that method of training, and is becoming stressed.

This owner may want to consult a vet. A dramatic change in behavior, especially one relating to biting, could be indicative of a medical issue.

Since this is a behavior change, I would first rule out an physical issue such a thyroid imbalance. Get thee hence to the vet with your dog for a work up including blood test including thyroid.

If the dog is fine then think about this. If the owner is leaning over the dog to put the lead on, that could be the issue. And, of course, the owner backs off so to the dog's way of thinking the behavior has worked.. so the dog will continue the behavior. I would get a simple slip lead and stand up and drop the lead over the dog's head and go on out.. no leaning over the dog.

The other issue of biting when the partner comes back down after a shower seems odd.. but, again, if the partner pays attention to the dog, talks to the dog, leans over the dog and biting makes the partner back off, the dog has again reinforced that biting works.

The object then is to be smarter than the dog. Confine the dog to a crate while the partner is upstairs taking a shower. ONLY after the partner is down stairs and doing whatever comes next, the owner should let the dog out of the crate, drop the slip lead over the dog's head, get her out for a potty run and then bring her back in. It breaks the routine. The partner should IGNORE the dog when the dog comes back in. See if that helps.

Sometimes we have to simply change the conversation...