Do you have other friends with kids so that you could all catch up in a group? That way there will be more kids to play with so your friend's DD won't be in your DD's face all the time, plus your DD won't feel so put on the spot. Maybe someone who has a boy the same age as your two DDs? While it's hard to tell never having met this child, it could be that she does have developmental issues, or it could be that she is just a rough tomboy and maybe it would be more appropriate for her to play with a less gentle child?