Fluid on cheek?

[Wildforestpony18]

Well, i've been told by another livery (friend) that it's just from grass but I wondered what you guys think, my NF has a bit of fluid on her cheek, its on both cheeks, and it went down a little bit after i rode her. All I can think is that she has been on a 'diet' paddock, but yesterday we put her in a field with lots of long grass for the day, and then back on 'diet' paddock;so could it be her glands flaring up? what do you think? she is fine in herself and she lets you touch it fine, no flinches etc.

Thanks for reading. x