Congratulations on getting the job. If you are looking to save on child care, then a term-time job is a great break. You should take the job: it will build your confidence, help you squirrel away more money and, a bit further down the line, when your daughter is older, it will help you get the next job, which will pay you more.
You don't say if you're married, and I really don't know whether that makes a difference in terms of what you can claim - but you may be able to get a share of equity in the house, financial support for yourself and daughter, an agreement that your husband pays school fees until the end of prep school as part of the financial settlement. See a solicitor and find this stuff out.
The school might offer a bursary to help/cover fees if family breakdown
is the reason and they want to help support a pupil's welfare. Make some discreet inquiries and emphasise the need for confidentiality.
Go to a CAB and find out what you might be entitled to in terms of benefits.
Find out what rent will cost and how much you will be expected to put up front. Draw up a budget.
You see the common thread here, don't you? Do your research and make a plan. Don't base your decisions on an anonymous forum.
Good luck. You've done really well so far, keep at it. PLAN!!