So I think I'm a little dense. Stella was being fussy, and kept pointing at the fridge. I showed her the pictures on the fridge and then took her away from the fridge, at which point she threw a fit. Then I held her on my lap at the table and she pointed at her high chair. I put her in it and she was happy for thirty seconds, then fussy again. I decided to change her diaper and she cried and she started doing the sign for milk. "Oh, she must be hungry!" I thought there was no way she was ready for snack since her lunch was just 3 hours ago, but I guess she didn't feel like sticking to her 4 hours between lunch and snack schedule. So I fed her and she's happily and greedily drinking her milk right now. Hopefully she'll stay in a good mood now.
It's amazing how communicative she's getting now. I just have to decipher what she's doing!