The thing to ask yourself (and answer very honestly) is: do you see yourself happy long-term in a poly relationship?
If not, wanting monogamy is absolutely valid and legitimate. Then, I'd say, even if you really like her, don't go forward. Love is not enough to sustain a happy relationship, and it will hurt both of you.
If yes, it is possible to be happily poly with anxiety. I'd recommend looking for (poly-friendly) therapy, and urgently checking out the books Polysecure and the anxious person's guide to non-monogamy.
I like your comment very much, but there's only one thing I'd like to add:
> but that is typically less apparent to the mono so the "due diligence" rests with the poly
I am not sure I fully agree with the conclusion here. I mean, yes, it is less apparent to most monos, and I think it is always the best policy for poly people to choose to avoid dating them. However, I think the responsibility for the decision of starting a relationship is equally shared by all involved, provided full disclosure was given from the start and there was no coercion.
Another resource for the mono perspective is the book Mono in a poly world.
Poly secure is a great book on attachment. I’d recommend listening to the audiobook or reading your own copies and then discussing after each chapter. Nonviolent communication and regular check-ins/debriefings can also be very helpful. And to be honest, if someone doesn’t really know what kind of additional relationships they want, people are going to get hurt. Boundaries are very important. What I found helpful was making lists of deal-breakers, needs/must haves, and nice to have but not essential and sharing it with my partner. This let him know my boundaries even if he couldn’t state what his were about others he was seeing. Boundaries are what you control about yourself to feel safe and secure. Rules are telling someone what they can or cannot do. For example, saying I will not have unprotected sex with anyone having unprotected sex with others doesn’t say they must wear a condom with other people. It states what you need to have if they want to have sex with you without wearing one.