Diaper off

Hi mummies! My 4 year old has been potty trained for quite awhile and I’m planning to let her go diaper free when sending and fetching her from school (Nursery 2), but I’m not confident. What should I do if my girl wants to pee and cannot control on the way and back from school? I’m worried she peed in bus also cos we took bus home from her school. Any experienced mummies can help me? Thanks.