My daughter just lost her front milk tooth. She is not even five. Is it okay for her to lose her milk teeth so early?

In general, the first teeth loss could be as early as 4 years old and as late as 7. And it would usually start with the lower centre teeth (as those are commonly the first to emerge). Then, there will likely be another round when the child is 5 years old and continue till all the permanent teeth have grown out (likely stop around 13 years old). Here's another article which you may find useful: http://sg.theasianparent.com/tooth-loss-in-children/