Instead of focusing on what goes into the applicant's mouth, you should be focusing on what comes out. In order to be a promising applicant, she must have had some good things to say regarding her experience, training, goals, and possible fit with your company. For you to immediately pass on her because she is a vegetarian is giving in to your personal biases.
Obviously, if she is a militant extremist who went into a nonstop rant about the evils of eating anything other than plants, then this is a different matter. However, that applies to any applicant who goes into an extremist diatribe during the screening process, regardless of the cause. It sounds like this applicant was pleasant, knowledgeable, and presented well.
As should be the case for any applicant, you should meet with her more than once, have other key managers and team members interview her, and then contact her references. And for one more piece of food for thought, it is important to remember that the best predictor of her future performance on the job is her past performance, not her diet.
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