I understand the ' as long as it takes' approach to some extent. Our current cleaners come as a team of 3. They've been us with for 3 years and because they know the house, the layout etc they can whizz round in 45 minutes (so 2 hours 15 minutes, rather than the 3 hours I pay them for). But they haven't raised their price in those 3 years, and their reliability and thoroughness makes them well worth hanging on to. I'm not going to quibble over 45 minutes when they do exactly what I wanted them to do.
To be honest they are a powerhouse, wiping down kitchen door fronts etc, always looking out (and upwards) for cobwebs or fingermarks. They arrive, get to work and don't stop until they leave. They have their blind spots (don't we all) but it's no skin off my nose to spend 5 minutes dusting an overlooked corner.
Our previous cleaner (with us for 6 years) was a lovely guy - came for the whole 3 hours but when he chatted to me his hands stopped. So I probably only got 2.5 hrs anyway.
I also think cleaners are more efficient in their work than I am. Before our cleaners come dh and I have a tidy up, so all surfaces are clear, clothes are put away, clean bedsheets are set out ready for them to change etc. When dh and I do the cleaning we are simultaneously cleaning and tidying (so it takes much longer), plus we get distracted by various odd but unnecessary tasks.
That said, @BoldAmberCat your cleaner is taking the piss charging £75 for 1 hour.
Were you clear about what tasks you expected her to do? Wipe down the skirting boards, mop the kitchen / bathroom floors, change the bed sheets, hoover under furniture, not just around it...