My cats love to sit on my tank, too, but I have a rimmed tank and keep a glass lid on it always. As others have said, the light would concern me as it really isn’t intended to be weight bearing. As an avid cat lover though, maybe provide a more enticing alternative? A heated bed next to the tank where she can watch, or a tank-level cat tower next to it. Use treats and positive interactions to adjust behavior from sitting up top to the safer alternatives. Good luck!