Oh yeah! She will for sure be able to get some grass. They quickly learn how to make that sucker work.
My boy gets excited when he sees the grazing muzzle coming now. He spends days in the dry lot and gets his grazing muzzle to be turned out on the grass over night. I put a baby carrot inside the muzzle so when I slide it on his face there is that treat in there. Now he comes to me to get his muzzle on instead of me having to go to him.
Yes they can get grass and they get very creative but just be sure that he isn't getting a sore on his nose as our foundered pony did because he didn't know enough to let up on the pressure and just wanted as much grass as he could muster through the openings.
Watch out for your horse chewing on, breaking pieces or widening the hole at the bottom of the muzzle. Mine are very creative at thwarting the muzzle and can modify them to the point there's very little grazing restriction.
We have patched the muzzles with inner tube patches successfully.