My female zebra’s left eye is getting smaller

[Zebrafinch000]

One of my lovely female zebra finches is closing her left eye quite a bit starting yesterday. It’s relatively smaller than her right eye (which looks fairly normal), but I have no idea why. It’s not swollen or anything and it’s not like she feels uncomfortable but it’s not opening wide enough. However, his particular finch has been having health issues (leg issue especially her left one) for a while and recently she’s been getting worse. She can no longer perch. Im bringing her to the vet tmr but I wonder if any of you know what could be causing her eye problem? Also, some of the feather near her beak fell off, but I’m not sure if it’s relevant.

Any opinion/advice is appreciated, thanks in advance.