I'm not being meaning to be out of place here or anything but I read that link you gave and if I read it right, which as tired as I am I might not have.

It say at 5 weeks start to take the mommy away for awhile then wait another week and total seperate them and in other 2 weeks get the mother spayed. That adds up to 8 weeks Right? Thats why I said to call the vet now, around this time she could and most likely will go into heat again

Then the other link says wait 10 weeks or if you leave it any longer she will probably get pregnant again!

Thats why I suggested that she call the vet, her kittens are 8 weeks old so by the time she get her into the vet it should be a good time to get it done.

As for waiting for the milk to dry up, yes thats good but I never had a problem and my vet has always told me it's fine, not to worry about that. Now you have me wondering about it and it looks like I'm going to have to question him again about that.