Consistency is the main thing here and breaking the cycle.
Your DC knows that if she cries for long enough, you'll give in and she'll get what she wants.
If you really mean to get her back in the cot, you're in for the long haul- about 4 days to a week or 10 days to break the habit of coming into bed with you. It will also help her to put herself to sleep without needing you there, if she wakes in the night.
You could still have her in your room, if you think it would be gentler, but keep putting her down in the cot and pat her and say shhh. If she gets up again, put her back down with the patting. This is very repetitive and the first night will be the hardest- no sleep for you I'm afraid!
Whatever you do and no matter how tired you are, you must not take her into your bed. Keep putting her down in her cot. Hopefully she'll eventually tire out and go to sleep, but as I said, the first night is the hardest and you'll be up constantly.
The next night, do the same thing-put her down in cot and when she cries, go and put her down again, soothe with pats and shh and then leave for 1minute. If she cries, go to her after that minute and pat and soothe. Each time you leave, leave it just a little bit longer before you go back to soothe her- do not pick her up to do this, just lay her down in cot each time. Do not give in.
Keep doing this and hopefully by day 3 or 4, you should hopefully have her sleeping in the cot....but it can take up to a week especially if she's been sleeping with you for 18months.
Good luck and persevere! Don't give in! No matter how tired you are! Otherwise you could go sleep in the spare room?