Not rude at all! That said I would approach her without your dog (or with your dog very calm) at first and just let her know there's another service dog there. People sometimes haven't told me and I've spent a few minutes trying to figure out what my dog was trying to sniff.

No, not rude at all. Friendships often start through shared interests and other similarities. You guys may find both dogs distract each other at first, though. Something to watch out for.

I've made several friends because of our dogs. Go ahead and say hello! :) I bet the dogs have seen each other already, heh. They tend to do that in my experience. Just make sure you approach her when she's standing still and not on the move so you guys can talk and so everyone is safe.