K.V.
Two year olds LOVE to dump things! It's great fun for them to see cause & effect. She might also be getting a kick out of your reaction to the spill. It's typical as well as a developmental stage for kids at 2 to dump things over. I'd say her fine motor skills just aren't developed enough to skip sippy cups or cups w/o lids. Since I don't have a dishwasher, I always choose sippy cups w/simple 'plugs.' When my older son hit 3, I started keeping the cups from the kiddie meals at restaurants & have bought bendy straws for him to use at home. Even tho he's 6.5 years, he still uses them, unless he's at the table. So, let her use sippies for a while longer & save your carpeting as well as your sanity!