2 1/2 year old now is Not sleeping through the night

LL

My LO is 21/2 years old. She has always been a great sleeper. Within the last 3 weeks she is not sleeping through the night and is constantly waking up between 2-4am. Not sure why and what I should do. HELP! This momma doesn’t know what to do. Also, she is refusing to nap as well.