i don't think you need to be there when the carer comes, checking what they do etc!
If your friend is happy with the arrangement and price, that's all that matters really, As long as the person isn't passing themselves off as a nurse when they aren't one. If the friend thinks they want to pay less/more then get some quotes from agencies for them - all you have to do is look in the yellow pages under nursing agencies and ring them up and ask.
It's nice that your friend has someone to worry about them but unless they are unhappy, it's nothing to do with anyone else really. Even if someone were superfit, if your friend was stuck in the bath for example, one person wouldn't be able to get them out anyway - sometimes it's just the comfort of having someone there to call for help if needed