- if we take her on on a year's contract (have been honest and said it might be a year but it might be longer) do we need to pay any kind of redundancy at the end of it?
No. Only if you keep her on so she works at least two years, and it is only a week (or a week and a half for older employees) a year then.
- she is going to work term time only. I will pay her for 39 weeks plus 5 weeks holiday. Is it reasonable to expect that she doesn't take holidays during term time?
Yes. But you will find a bit of flexibility on both sides is in everyone's interest, so if she has a good reason to want a particular day or two off in term time you should listen.
- She is fully registered and 'checked' officially. On checking references myself, is phoning previous employers enough?
Probably, but if you are not absolutely confident after the phone calls and checking directory enquiries for the number (and if ex-directory checking the area code makes sense), write to them to check the person you are speaking to is the person at the address.
Perhaps overthinking things, but isn't this easy to 'cheat' on, ie just get a pal to answer the phone? Now I am going with instincts here and don't think for a minute she would do this, but I am just the over cautious type.
See above.
- we have chatted about discipline, food, activities, driving, first aid and general duties. Have I missed any definite areas to ensure we are compatible?
The most important thing is that she is "compatible" with your children. Have you seen her interacting with them?