Its probably worth talking to your girlfriend and actually asking her what she eats and will not eat and what is the basis for her decision. It is surprising how variable the term 'vegetarian' is applied across people. I know some people who are die hard vegans and will not eat out of the same pot that was used to cook meat. I know other vegetarians who regularly eat fish or will on occasion eat chicken.
There is the whole confusion of the term, because it is applied to convey 'health eating choices' or a set of ethical and moral values. Some vegetarians gravitate to one or the other and unless you ask them outright they rarely declare which side of the fence they are on. Being this is your girlfriend, you are likely to get in trouble either way