Go according to your comfortability. I would get a general card and maybe some flowers if you will see her that day. If not a general card from you will be sufficient. You don’t have to get anything mushy as you and her haven’t built a relationship to that yet.
Once you’re in an established relationship if your boyfriend is comfortable with the idea you can always sign your name to his card and chip in for her gift.
Keep it simple, and give a small gesture of her being a mom. When I dated I would usually do the same unless a relationship was established than I would get more creative in my gift giving approach.