Welcome to the forums!
There can be a few reasons that explain the baldness on the area and sinus infection could be one of them.
Does your budgie girl exhibit difficulty in breathing? This can be noticed by a pronounced, rhythmic tail bob and sometimes a wheezing sound while breathing.
Does she have wet sneezes and have you noticed a steep decrease on her appetite and energy levels? Has she been scratching her eye a lot and is the other eye also missing feathers?
From that pic I'm unable to tell if the area surrounding the eye is really swollen or not.To me it doesn't seem swollen, I also fail to see teary discharge from the eye. The nostrils also appear to be clear.
It's possible that the temporary baldness on that area is due to a moult, budgies also moult those tiny feathers surrounding the eyes.
Still, it's good to keep a close eye on your budgie, if you notice she is having discomfort on the area and she appears to be affected by it, then the best thing to do is to have her checked by an avian vet specialist, so that she is correctly diagnosed and treated.
Best of luck with your budgie girl!