I'd guess that she does it because she can! It sounds like a new thing she's figured out how to do, and even better that it gets your attention. I'd end the meal when she does it, even if she hasn't eaten anything. Don't make a big deal out of it, just matter of factly say something like "It looks like you're not hungry now, we'll try again later" and take her out of the high chair. A lot of times when you stop making an issue out of weird food behaviors, they stop on their own. Of course, it could be teething too, but I'd still end the meal as she isn't eating anything anyway.
One thing to keep in mind, there's a huge decrease in appetite that happens around 1 yr, so she's going to start eating way less than she used to. It's normal for toddlers to go for days without eating barely a thing. If she starts dropping weight or waking at night from obvious hunger, then check back in and we'll see if something else might be going on. Don't worry...healthy babies don't starve themselves!
