I have a variation to have 4 small children, and I do get comments from people who know that we are usually only allowed 3.
We've had discussions before about how many children a CM could have and, even with an agreed variation from Ofsted, none of us have ever heard of anyone being allowed to have 5 under 5s. The nursery children will not be counted as 5 year olds, as they are both part-time. Again, even if they only overlap for half-an-hour, it is still a little unlikely that Ofsted would allow her to have five children by herself.
However, could she have had as assistant with her? If so, she may well have been OK.
Another explanation is that there may have been some kind of emergency and she was going to be temporarily over her numbers.
I don't like the idea of getting another CM into trouble. However, I know of a couple of childminders locally who have been renowned for regularly doing things they shouldn't. Nobody wanted to snitch, but sometimes it has to happen as their general practice (there were other safety issues) was putting small children at risk.
I think you should have a quiet chat with your friend.