with respect, its not that difficult. if she was coming with you to help look after your kids on a day out (adult entry) that that is your expense, not hers, like any other job, and if not then you should make that clear. presents/flights etc are your choice and nothing to do with it.
go onto a local website and find out what a lodger, not a tenant, would pay. and to calculate food, divide your current family food bill by the number of people in your family. if you are serious about elec etc, then do the same with your bills.
i'm sorry - but i find this really problematic. the deal with an au pair is that they trade some help with your kids/cleaning for board, lodgings and some time to study the language. they arent cleaners and nannys for people who wont pay the going rate. if you want a nanny, or cleaner, then pay one properly.
minimum wage is £5.52ph.
www.hmrc.gov.uk/nmw/#b
also: www.aupair.uk.com/FamilyHelp.asp
What are the differences between an au pair / au pair+ and a nanny?
Au Pair (Live In)
Works a maximum of 25 hours a week and a maximum of 2 evenings baby-sitting for a minimum of £60 per week
Family gives full board, own room and two consecutive days off (these do not have to be on the weekend, but with the au pair's previous agreement)
This type of applicant can look after children of school age and is not qualified in child care. They can only look after babies or children under school age if a parent is at home and the level of responsibility should be kept to a minimum as English is not the applicant?s first language. This is for the safety of your children
The applicant comes from one of the 27 EEC countries, and does not require a Visa to au pair in the UK. However, applicants from Turkey do still require a Visa. On our site, Turkish applicants should already be in the UK, or have gone home for a period of time, but in possession of a valid au pair Visa. It is the family?s responsibility to check the applicant has a valid Visa and is allowed to au pair in the UK
An au pair can look after children, O.A.P.s, help you get around if you are disabled in any way