You can gift any individual $15,000 per year without any tax implications. Jill could gift Bob $15,000 and also gift his wife $15,000 and stay within the rules. She could also do that over a period of time.
So if Jill wanted to give Bob $90,000, she could essentially do it over 3 years without any tax implications. That’s my understanding at least. But this gift cannot be a fee for these services. It has to just be a gift out of the goodness of her heart. Bob can’t charge her or specify an amount. That would be illegal.