I recommend Hipline near Lake Merritt, which offers very fun dance and fitness classes for women. 

They're a self-described "judgment-free space" and you'll see all ages, colors, sizes, and fitness levels. As a middle-aged woman, I always feel welcome. I also like that the dance classes are more about shaking it than nailing the choreography.

The studio is next to Trader Joe's and parking is available in the TJs lot. They also have in-house daycare, though I've never used it.