Robert, first the legal part. Did you get her to sign a release. If you did, then legally you need to do nothing. If you wish you could reassure them that you will not ever post them or show them in public.( the nudes)
But with a release the property is yours and they have no claim to them, if she was paid in money or prints.
If you didn't, then it can get sticky. I personally would forget the friendship part as they are now not your friends anyway. You have to decided how much you really care about the prints and negs, and if you don't really care that much, I would be tempted to destroy them. I would not under any circumstances give away my negatives. Keep them or destroy them but never give them away.
If they are important to you then you need to make the decision to fight for them. Sometimes fighting can cost money, friendships and frayed nerves.
The clincher is the signed release. If you didn't get one, plan to in the future.
You made a comment about being "professional" and part of the is sticking to your guns on a matter that your profession requires. That what you shoot is your property and nobody elses.
My 2 cents worth...