To answer a lot of your questions, no, we did not know of this before she was invited. Also, I guess she won't eat anything that someone else has touched. I don't think my daughter knew this of this girl ahead of time because my daughter mentioned about going to the restaurants and this is when her friend told her of her situation! This was after she had already booked her plane ticket!

I believe that this girl plans on eating in the timeshare by making her own food (things that other people have touched)!
I imagine it irritates the heck out of you. Even with the insight I have from my own issues, it would irritate me too. This girl is an adult, or close to it. She MUST have realized that on a vacation, restaurants could come into play. She really should have let you guys know up front before she spent any $$ or even accepted the invite.
I am sure it may be somewhat embarassing for her to share her issues, but if she needs special accommodations, she must be willing to explain and ask for them. I would sit down with her or ask your daughter to, and find out exactly how she expects to eat and/or what her own parents/family would do in this situation. That will tell you a lot.
For me, my DH and kids would make restaurant reservations. If I could not bring myself to go, I would be free to go back and cook something for myself and come find them later. My family makes some accommodations, but only to a point. They don't miss out because of me, and I would never expect them to.
If her parents, however, always make sure to cook for her in the room and just did not ever go out to eat because she couldn't, then that is a different story.
If her experience is like mine, she knows you will have plans and will go through with them. If she does return to the room to make a sandwich or something, she will most likely not be overly hurt if she goes alone. I know I wouldn't.
If her parents are like the second example, then you may have problems. Because she will most likely expect at least your daughter to always go back to the room with her.
While I do empathize with her issues, I just cannot imagine accepting an invitation like that, knowing my limits, without first letting the host know exactly what was going on with me.
One more thing: Yes, other people have touched the villa stuff. Her fears may not make any sense to you. They may not make any sense to her. I cannot drink out of the same bottle as DH...the man I kiss. Not sure why that is.
Good luck.