Gay is also called gay. If this girl tells her that she is gay, she may really be gay, but she may also want to refuse you, but in either case, it should be a signal that you have no chance.
I liked a female colleague in the company before, and that colleague also said a lot of rejection words to me, for various reasons, similar to this. Maybe this girl found out that you like her, and she was afraid that her reason would not convince you, so she used a more malicious reason.
If girls are really gay, they should also look at each other with a positive eye, respect each other's sexual orientation and be ordinary friends instead of lovers. I wish you happiness!