Someone posted a funny pic from the trailer in another thread, so I'll re-use that (too lazy to screen cap my own)...
Soooo....yeah. No real chance of perspective issues, here, as you have a catwalk we are looking straight down to compare against. The TIE cockpit 'bubble' looks like it would easily fit between the rails of the catwalk. And you can see how large Jyn is compared to it, too.
And remember from the cast photos (as well as her real-life person)...she's already actually kinda on the small-ish side...
I mean, geez, could you even fit one of those X-Wing pilots into that TIE cockpit??