Did you see Mashi's post about the rice, pasta, beans activities? I am going to go out tonight and buy some and dye the rice rainbow colors with food coloring so DD can scoop, pour, sort, mix, etc. I think she'll really like this.
I second babydolls....DD plays with hers for hours. She feeds them with spoons and bottles, swaddles them, puts them places to sleep, pushes them in a small stroller.
She also loves watching Calliou...which we let her see maybe once a day on demand. I think it's 3 10 or 15 minute segments...so 30-45 minutes at most. I save this often for when I need a shower, but baby nap time might be a good time.
I googled some ideas and there was one about hanging large paper or an old white sheet outside and letting them use food colored water on paint brushes or in a spray bottle to decorate. That sounds fun.
For bad weather days, let's see....how about some food fun? Making a fruit salad or ants on a log.
You could let her use shaving cream in the bathtub or on a cookie tray to "finger paint" (I heard you can mix this with food coloring also to make it more fun)
Do you think she'd like dress up? My DD loves putting on my shoes, etc. and I was thinking of getting her some old hand-me down grown up things to play dress up. Big beaded necklaces, hats, shoes.
I hope some of this sparks some ideas! You're making me feel good because DD is pretty good at entertaining herself

sorry.