Aqiqah of child is mustahab. If you could not perform the aqiqah of your daughter as you were not aware of it then you shall get no sin. The mustahab method of aqiqah is to do it on the seventh day of childbirth. But, if it was not done, then on fourteenth day and if not then on twenty first day. After passing 21st day there is no restriction of days. You can do it when you wish. Now if you want to do aqiqah after six years, you can do it. The mustahab method of girl aqiqah is that one goat is slaughtered and its meat is distributed among relatives, near ones as well as poor and needy ones or they are invited to meal. It is right to eat the meat of aqiqah like of Qurbani meat.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband