Toilet Refusal

DD1 is now 3 1/2 and has been TT since she was 2. She always had a small wet patch in her undies, but would then run to the toilet without issue. We never made a big deal about the wet patches, just changed her undies if needed.

But over the last few weeks she has just started weeing and pooing in her pants. It's not that she is getting distracted and forgetting, she is actually working hard to hide the fact that she's wet, like walking sideways so I can't see her bottom. I would see a wet patch and suggest going to the toilet and she would refuse. She will even sit on the floor going red in the face trying to hold it in. I've had her checked by the Dr for UTI and he has found nothing wrong. I've done my best not to get angry with her, I've tried talking with her about it and I've tried reward charts with no success. I'm really not sure where to go next. Can anyone help?