Not sure how far you want her driving but some of the rec ctrs in moco have weekly indoor play times. There is definitely one in Burtonsville at the Praisner Rec Ctr. 3 mornings a week they get out a bunch of toys on the basketball court and the kids can just play, for free. They have balls, a couple of slides, ride on toys, push toys, that kind of stuff.
I want to say someone told me there is one in Wheaton but im not sure of the name of the rec ctr. You could probably find out though.