
Our boy started losing them around that age and kept on losing them till around...5 nearly 6 months old :)
(Ive even kept them as well LOL :) )
I think hard chews when supervised are ok, but the usual puppy toys are usually suffice until their baby teeth are lost, when she has lost her baby teeth she will be needing serious chewtime so that would be the time to upgrade but if she is happy tucking into an older dogs chew (which is probably already softened by the older dog) then let her, just keep an eye on her for bits she may break off or try to eat :)