The rate of pay she is suggesting is an insult and less than half of minimum wage, with no benefits, no pension, no sick pay, no rights at all, is she going to pay you on the 13 weeks off? If not then your much lower wages also have to cover that time, what would happen if you were sick or she lost her job etc
You should get at least £1280 every 4 weeks, what is she currently paying for childcare, she should also be providing food for the children and the free hours she is entitled to would be lost unless you were able to take the 3 year old to nursery, which has other benefits for the child.
Think very carefully, not least of how it would change your relationship with your daughter, to employer and employee