With all due respect, Ameriscot, I disagree with your job description of au pair and nanny. There exists (or at least used to exist) an au pair visa which restricts what that person can do in terms of there role as an au pair and how many hows they can work whilst in the country. But, times have changed. And, an EU national who is hired as an "au pair" is subject to the very same employment laws as any other employee in this country. Majorstress, you can hire anyone you like (within the law of course) and ask them to work however many hours you choose, and assign them whatever duties you choose (so long as they agree to them, presumably in the contract), and you can give them a job title of "au pair", "nanny" or "ambassador to Charlie Brown" if you like. There are of course employement restrictions on non-EU residents that restrict you further.
Also, if an employee lives in your house, you are not required by law to pay them minimum wage. Although, you will find plenty of mumsnetters who pay their "nannies" more money than I could even consider. If you want to know what you can and can't do as an employer, I suggest looking at www.nannytax.co.uk (I think that's the right address?). It is very unformative. Also, a lot of people tend to quote what the agencies say are going rates. Personally, I think these numbers are inflated. I don't think people like me who avoid the agency to save money are taken into account when they run their numbers.
A CAT is a way to send me a message through mumsnet. It stands for Contact Another Talker. Link at the top of the page.
Regarding the hours, if she works until 8:00, as she is contractually bound to do, she works a 29 hour week. I know people who work double that. Also, I don't think the schedule of breaks is too unreasonable. Yes, she has a two hour break where she can't organise much of her own activities. But, aren't you paying for an English class? She could use that 2 hours to study. Seems reasonable to me.
As far as the +cleaning goes, I have assumed in my comments here that she has the time/ability to do this cleaning in the hours you list. For example, nap times, or times when your DDs are watching TV or otherwise occupying themselves. Granted a two year old can't be left alone for two long. But, I think it's reasonable to expect the au pair to say fold the laundry in the same room whilst they watch Winnie the Pooh.