B.Z.
Is she teething or otherwise going through some changes?
This is probably a sign of separation anxiety. Your daughter's developmental stage is such that her memory is increasing and her imagination is starting. Please please please don't make her fears come true by making her cope on her own, crying and afraid that she's alone.
I use cosleeping methods, so my experiences won't work the same for you. However, when my son was around 14 months, he was willing to try out new techniques rather easily. Mix things up by putting her mattress on the floor in her room with a gate at the door. Or continue the current situation for another two or three months until she's transitioning into a new developmental stage. She will be less willing to try out new things after 18 or 20 months old, but it's not impossible to make changes at that age or older.
It's possible that your daughter is simply telling you that she needs more frequent reassurance from you that she is safe and loved. You might try some different techniques during awake times.
Best of luck!