Dog afraid of people meeting dog afraid of dogs....

We have a situation to deal with this weekend for which I could use some advice. We have friends coming over with their dog, which is normally good news for us since Poca's fear of people is helped when new people have a dog with them. But this dog hasn't been socialized much and is afraid of other dogs (except the other 15-year-old one she lives with). She's ok with people, not great, but ok. And she's reactive so I know she'll snap if the pressure gets too much.

So my question: what would be the best way to introduce them and get them used to each other? Poca's first reaction will be an elaborate play bow, whining, and straining to say hello to the new dog, while barking a warning at the people she's afraid of. The other dog from the sound of things will cower, freeze, try to run away, and if overwhelmed, she'll probably try to attack Poca.

Numbers: Poca is a 65 lb shepherd mix. Angel is a 40-50 lb shepherd/chow/rottie/lab mix.

It's not much to go on but it's all I know about the other dog. Any suggestions?