Help!!! I found a growth on my budgie's tail?

Recently I found a growth on my budgie's tail, well, it is just above the tail. She seems fine though, I know they hide symptoms. I read that it is a preen gland or something but it wasn't very helpful. She is not finger tamed but I have been working on it and I'm so close! I can't loose her now! I had 4 budgies, but 2 of them died from medical issues which I can't get over. I've been working on getting her out of her cage, I've been leaving the cage open in a bird proof room, while I'm there, so she can come out willingly. But she lets me pet her a little. I don't want to force her out, but I don't want her to spend the rest of her life in a cage. I want to slowly and gently grab her and take her out. I'd leave her on her cage and talk to her, (she isn't clipped but I want her to get exercise by flying). Would that be fine? I want her last few months to be happy, even if the growth isn't fatal. please help, im very sad and dont know what to do.