If she stays over the asked for 6 weeks , would it now affect any subsiquient applications ??
No, it's valid for 6 months, what it says on the tin. She should go back a week before it's end though, makes it look good for future visa's.

They only do 6 monthly Visitor visa's, which is why you go one for 6 months.

...and if anyone wants to know the reason for her being granted a Visitor visa, as mentioned elsewhere, she owns a business, and has kids to go back too.