Unfortunately, nanny-parent relationships are far more personal than most employee-employer relationships, and a LOT of details affect how one handles various situations.
How old is your nanny?
Has she ever been a live-in nanny before? If so, what did her references say about sharing space with her?
Why do you need a live-in? (Early morning starts? Inconvenient location?) Are you open to the idea of hiring a live-out nanny, either her or someone else?
What did you say/how did you handle it when she borrowed your clothes without asking? How did she respond?
I have a difficult time picturing a new nanny being WORSE than your current one, but the questions above are the kinds of things to think about when you're looking for her replacement. If you absolutely must have a live-in nanny, you'll want to hire one with live-in experience. (Experienced nannies cost more than inexperienced ones, so plan for that.) Make sure you ask their references about sleeping habits, social habits, anything that you didn't realize would be an issue before hiring your current nanny - listen carefully to what they say AND what they don't say, as some people are reluctant to badmouth past employees and will instead simply refrain from saying very much that's positive. Also think about what kind of boss you are/want to be and if it doesn't come naturally to you, as it doesn't to most people, practice your managerial statements in the mirror or with a spouse/friend/sibling. The more calm and comfortable you are in addressing issues, the more easily they will be resolved (most of the time).
And to answer your question - yes it is worth going through the hassle of finding a new nanny! MOST nannies will treat your children well, most will love them, in fact, and they will adjust quickly to her replacement, but YOU also need to be happy with the person, both because she is your employee and because she's living in your home. Don't have any advice on the actual process of letting a live-in nanny go, but hopefully others will be able to advise you on that. Good luck OP.