Keep boundaries. Set boundaries. Like maybe agree to meet once a week for X-activity (a games night or something that could have a rotating day and location based upon how everyone is feeling?) Maybe talk about it with her if she acknowledges that the two of you can set each other off? And maybe make an agreement that if someone starts feeling triggered, they will just say "I need to go" and then go home without having questions asked - it can be handled the next day, or not at all.

And buy some child-safe hand sanitizer (baby wipes!) and get that kiddo used to having his hands wiped after EVERY contact he has with his mouth or nose