my toddler struggles to settle at night

Help!! My daughter has slept since she was 5 months old. This past 2 weeks she has struggled to settle of to bed, shouting for me and her dad and crying. She goes to bed at 7pm as we need to get up at 6.30am. Shes always had a good routine. She can take up to 1/2 hours to settle off, some nights up again at 1am sometimes 4am or 5am, sometimes sleep through and wake at 6am. Could it be nightmares, seperation anxiety? Could a night light solve the problem? It could have been the fireworks that upset her, she suffers from constipation, but thats under control at the moment. Shes fully potty trained in the day, is she ready at night? Thing is she will NOT get out of bed, just shouts us and we go running because she screams that loud!!! Anyone got any tips or clues. Its hit us like a truck as we are not used to this! Thanks, Kelly x x