Modern fantasy book from around 2010. Possibly with a lesbian?

Read this probably around 2010. I think it was in the Young Adult section of the library.

Modern setting fantasy book about a woman who was from a family with magic. Her abilities developed late and she could only cast curses.

She made a deal with some spirit or something to help her control her curses and the thing followed her around looking like a mini version of her.

She had a brother that was nice to her. I know at one point she tried making brownies, got stressed out, and told him to shut his mouth which accidentally sealed his mouth shut for a few hours.

She also had an older uncle or grandpa who didn't like her much and thought her curses would end up killing them all.

The spirit thing was tricksy and at one point the main character saw a kid on the beach and wished she could enjoy the beach like when she was a kid, so the spirit thing turned her into her younger self for a while.

She might have ended up with the spirit thing at the end?