I had a similar problem, even though we didn't co-sleep. Around 6 months my daughter got sick so we started bringing her to bed with us. She got VERY used to that. What we did (although she had been in her crib in her own room since the day we brought her home) was spent about 3 nights with very little sleep. When she would get up, we would get up, rock her to sleep and put her back to bed. When she woke up again (rather it was immediately after or several hours after) we would rock her again and put her back in bed. We just wouldn't put her back in our bed, even if we were up all night. I think it took 2 or 3 nights and she started sleeping in her bed again.
If I were you I would make a decision to either let her sleep with out or in her own bed and own it. I know, for myself, I will go back and forth and then realize 3 months of restless night have passed. If she is going to sleep with you...cool, she's sleeping with you. If not, then she's not. I've lost a lot of sleep over not owning my decisions =O)
Best of luck,
C.
Oh, almost forgot the separation anxiety part. My daughter is still going through this at 18 months. I remember reading somewhere that at around 3 or 4 it becomes all about dad. At my daughters 1st birthday party she wouldn't let anyone hold her but me. I finally made my husband (her dad) hold her and I played with her while he held her until she stopped crying and reaching for me. She got a little better with him after that.