Should I wean puppies early from aggressive mother dog?

I have a Chihuahua with a first litter of 4 babies by c-section. She is mostly good with them, feeds them, (I supplement with 2 feedings a day, as she has been a little overwhelmed by 4), keeps them squeaky clean, and is contstantly checking on them. They always want to nurse, and she has bitten and drawn blood on 3 of them so far. This has happened randomly, and without any warning. The puppies are 17 days old, and for a while I muzzled her when she was feeding them, or else staying right with her and keeping her away from their faces. All the bites have been on their little heads...and I have caught her snapping at one (early in the first week) but she was very sore, her milk was late, and she had two bloody teats from the puppies nursing so vigorously. I tube fed them for 3 days and they have been bottle feeding at least a couple meals a day ever since to supplement, as I was worried she does not have enough milk to feed them all. Should I wean them early?? How early??