Obviously flowers are always beautiful and a lovely gesture, here are some additional ideas that I have been either gifted or gifted myself (typical me) that I think would really show a new mom in your life that you are thinking of her. Personally, we are not allowing guests to see Oakley for 2 weeks to establish a routine for ourselves and I know many are doing that as well at this time- so the days of bringing a casserole over are somewhat a thing of the past (at least they aren't a thing of the present).
Also- it's important to ask how MOM is doing and not just about baby. This is something I never realized until becoming a mother myself! It shows you care about HER and how she is doing- it makes a world of difference!