Hi there! Your daughter needs to visit a local dentist for xrays and fillings or root canal treatment (pulpectomy or pulpotomy). The space made by the missing teeth should, if possible, be maintained using space maintainers. Also to prevent further decay I would advice cutting down in sugary food intake and religiously brushing her teeth first thing in the morning and last thing at night. Being 6 now her first permanent molars will soon erupt (they may have started erupting already). It is necessary for you to ensure that they do not get caries (decay). So brush properly and your dentist may also recommend pit and fissure sealants to ensure they remain safe. Hope this helps.

She has to go for decay removal and filling of it.. Visit to a dentist for it..