Hey L.,
Having a new nanny is a huge adjustment, as is going back to work and leaving your precious baby with someone else. We are on our fourth nanny for our 3 3/4 year old and we FINALLY found one that is everything we hoped she'd be: fantastic and a true member of the family.
That being said: your nanny is living in your home during the day, taking care of the MOST precious person to you. I remember feeling the way you did when I didn't feel good about our nanny, but once we found someone that we LOVED, I asked her what we could buy for her that she particularly liked to eat, because she's living in your home when you're not there, and you want her to feel a part of your family. You do not want her to feel resentful. Remember, too, she can take your baby and go grocery shopping when you're at work to pick up extra food, which wouldn't put you out too much.
We welcome our nanny AND her son (who comes over in the afternoons after kindergarten) to eat whatever they want to with my daughter.
If there's something in particular you don't want her to eat because it's something you're going to make for dinner or is a special treat for your husband, just tell her. Ask her what she'd like to eat and ask to her to put anything special on the grocery list whenever she wants something. Our current nanny loves Pepsi, and a different kind of mayo and a different kind of bread than we ordinarily eat, but I get it all for her, because we love her and want her to feel we care about her and are invested in keeping her happy and with us as long as humanly possible.
Part of it is a huge transition, but pay attention to how much of it is about how you feel about the nanny. If it were a different kind of person would you feel less resentful?? Maybe she's not the right nanny for you?