J.✰.
More than a smiple thank you would be a nice thoughtful "We've been friends since phones had cords! I am so glad we're friends. I am so very thankful for all that you do for me both physically and emotionally. Thank you so much for all of the effort you put into throwing me a baby shower. Baby and I are incredibly thankful for your hard work and thoughtfullness."
Maybe a friendship bracelet (might make her giggle), but since y'al are now adults, get her a nice gold/silver bracelet instead of a string friendship bracelet.
or invite her to be the first to come see you and baby once y'all get home from the hospital.