The real question is - even if your flatmate is liable for half the rent, and she doesn't pay, what can you do about it? Taking her to court would take a long time (during which you would still have to pay the rent), would probably cost you (even if you represented yourself without a solicitor) and even if you won she might not pay up. The best thing is not to provoke her but try to part on a reasonable basis. If you don't think a month is long enough to find a new flatmate, then perhaps you can persuade her to pay a couple of weeks more rent. (Won't you have paid a deposit to the landlord; and won't she expect half of that back? This might provide you with a bit of gentle leaverage, as you can't be expected to repay her until you find a new tenant.)