Bah! Lots of people sleep with their kids.
If you or your DD are uncomfortable with the transition, a half-way measure like pushing beds together or a mattress on the floor might be one way to go.
I slept on mattress on the floor with DS for aaaages. Then after his sleep started to settle down and he began to be able to sleep alone, we switched him to a single bed. Aside from falling out once or twice, he's been fine in there unless sick (when he comes back to bed with me). We still spend time getting him to sleep in the night, but it works pretty well.

Just give the gradually moving away approach a try and see how you go. You'll find out soon enough whether she's ready for it or not.

As for your DP - maybe try and set aside some special couple time too? Doesn't even have to be in bed.