When you first have a bunny, especially a teen that is ready to be spayed, they might pee and mark and generally lose their good litter habits from before. So be sure to book your appointment for her and plan to be patient for a month afterward while her hormones settle down.
Sometimes they have a preference for one type of litter over another. Some like pelleted kinds, like Aspen pellets, Feline Pine, Yesterday’s News; others like softer like Carefresh; and still others like shavings like Aspen Shavings. (NEVER use Pine or Cedar shavings, however. They are hazardous to their health.) I personally use a combination of Aspen pellets which absorb odor 4x longer than the others, and Aspen shavings which also let the pee go right down to the pellets but feels soft to her on top.
And, my bunny will go outside her pan when I haven’t changed it soon enough. “Hey, MOM! Clean up, here, will you?”