You could give her bicarb in a cup to play with. My kids have had endless hours of fun making goop out of it, they love to paint themselves with the paste, and love to paint the bath sides - which helps clean it.
This is brilliant why have I never thought of this!! I scrub the shower when I am in it. The kids would love it!!!
Also op I couldn't have bubble baths as a kid due to skin problems but every now and then mum would put a few drops of food coloring in the bath and once I was in drop in, what I always thought was flour but I think must have been bicarb, and I would get a fizzy bath.
It was so cool my friends always wanted to have baths at our house.