Honestly, when you terminate her, keep it short. The more information you give her the more wiggle room she'll take to try and squeeze herself back through your door. Be firm, smile and say 'I'm sorry but this arrangement is no longer working. Dcb's last day will be______.' Don't elaborate or explain or give excuses. If she keeps hounding you, stay firm, get firmer, and keep repeating what you just said.
If you need all of us here to be your backbone to help you do this then pretend we're all standing right behind you.
Imagine if you have to come back here and tell us you changed your mind, gave more time, couldn't do it, etc., etc. We might have to hunt you down and greet dcm at the door ourselves.
You've got this, really you do!! The first time is always the hardest! But the relief you'll feel and the self-respect you'll have after it's said and done will be all so worth it!!!