She's not that big because she just drank a lot of wine. The wine is buildig up inside her, filling like a water balloon from inside.
It doesn't have a very good taste, but it has something that made her keep drinking until she got drunk and didn't care about her belly swelling up, she only keep drinking from the bottle.

She shouldn't be able to react this size. She's waaay past her limits... There's going to be a huge mess to clean and she's gonna have a really bad hangover tomorrow.
Hope you like.