As someone has suggested, widen her contact points, be it an art session, library reading (no bad thing if they love books already), even playgroups and sessions in the park. She'll find little friends and if they get on, then think about a play date. Don't force it though, just let mother nature/fate come to you (all)!
Wait until your daughter is 5, has a playdate, and you are with her or his Mum with glasses of wine to hand, and your daughter decides to play 'make-up' and let's use Mum's Chanel!