Hi C.,
Our son did the same around 3 years. The only thing you can do is bring her back to her own bed and tell her she has to stay there. Sometimes you end up doing that 4 times a night, because everytime she wakes up again she will come to your bed again. This will take a while. It took my oldest son maybe even 6 months. Be very consistend, bring her back every single time, even if you're dead tired and it is tempting to let her sleep next to you.
Of course you know about giving her a sticker every moring when she has slept in her own bed for the whole night...
And we lock our door when we have sex. When one of our kids knocks on the door (very surprised that the door is locked because its always open) I put on a bathrobe, bring him back to his bed, lock the door again and we continue :)
I know of 3 friends of mine who put a lock on their childs bedroom door. Personally i don't like that idea. I rather wake up 4 times a night and bring him back. But if it works for you, just do it! Every child is different.
Good luck. Take a deep breath, it will take a while...
I.