My advise is to ride it out. She's going to complain for a while, but she'll learn to sleep alone. If you go in and lay down with her every night soon she won't sleep unless you do that and you'll have a new habit to break. This is probably a jealousy thing with the baby, wanting some special time with mommy and daddy. See if you can do some special bedtime ritual, stories, bath, painting nails.... This won't solve her sleep issues immediately, but it will build her confidence.
Kids are manipulative, they want what they want now. They are testing boundaries and learning what mom and dad will cave in for. This is part of parenting, teaching them to be independent and not need you all the time. I know kids who've been in mom and dad's bed or room for YEARS. Don't go down that road, it just gets harder as they get older.
Best wishes!