She said that she just wanted a one off clean first to see how good i was before she agrees to using me for regular cleans, so i am really wanting to remove it to get the business.
And then you remove it, spend loads of time on it for standard rate, and she says bye bye sucker.
So she wants to try you out to see if you're "any good". That would send alarm bells ringing with me. Many years ago, I even had one guy after a "free trial" for the first clean. I told him I was a window cleaner - not an internet service provider. We both laughed and it didn't happen.
I would be wary of this one. It sounds like she wants the upper hand from day one. As far as I'm concerned an arrangement with a customer is two people agreeing to give/receive a service on equal terms. If a customer starts showing too much sign of wanting control, I might as well be on the PAYE working for a boss.