Cat Peeing Problems

Please help 😞 I've had this kitten since September and before we got her she was littler trained and we have never had a problem with her not using her litter box since the past couple of weeks. I didn't really know it was her because it's been in the bathroom and I'm pregnant so I thought I was just smelling the toilet but it was the small hamper we have in there. I just now caught her peeing on a pair of jeans I had laying out that I was planning on selling and it's the first time I've caught her. I had no clue how to punish her because she's never had to be punished.. I don't know what's changed. Her litter box is clean, it doesn't have a lid on it, I clean after she goes. We were planning on picking up a new kitten that will be ready next week and I'm suddenly second guessing it because I feel like she will act out. Can anyone tell me what's changed or what I need to do?