Hi about 5-6 weeks ago my daughter( 2 )kicked my ribs, the bruise stayed purple for weeks, now it's red, warm and burns. what can it be?

Possible infection: It could possibly represent an infection and I would consider being seen. It sounds like you initially had a hematoma in which bleeding can occur into the soft tissues creating a "bruise". A hematoma is basically some degree of bleeding into the soft tissues and this fluid can potentially become infected at which time it will become red and warm. If it is infected it would likely need antibiotic