Debbie, 6 weeks is early but possible to be weaned at that age.

In fact our cat protection said that if you can catch mum in a trap you can get her spayed, keep her overnight and return to the outside and the kittens will be fine for one night alone at that age.

In fact poor Bramble had one night on her own at that age

The sooner you get her done the better or else the poor cat will be pregeant again.

It is like you are dammed if you do and dammed if you don't.

All the best