Well, obviously, spaying now would be dangerous to the kittens. Unless she's completely full term, spaying will result in the deaths of the kittens. But if she's truly 8-9 weeks along, she's full term, and you should still be able to save the kittens if she's spayed. Spaying might be slightly more dangerous to the mother during pregnancy because there is extra blood flow to the mammary glands, which will be right around the incision. However, the risk isn't very signifantly greater.
Personally, I don't believe in aborting kittens. It's a bad situation all around, but I feel like they should at least have a chance. If you choose to spay her now, and the kittens are far enough along that they survive, you'll have to prepare to handfeed them. The mother can still nurse them, but she will probably not feel up to it for a couple days. Then she may lose her maternal instinct and refuse to care for the kittens altogether.
Handfeeding kittens is a huge challenge and can be heartbreaking. Very often, you will lose some kittens. For one, if they are hand nursed from day one, they miss out on the colostrum that mothers produce for the first couple days. This is richer than breast milk in nutrients that help the kittens grow strong. Second, they are not getting the antibodies from the mother's milk to help them fight off infection. Third, some kittens just die of Fading Kitten Syndrome, which is similar to Sudden Infant Death Syndrome. There's no known cause of it.
Newborn kittens absolutely must eat every two hours, including during the night. As they get to be a few weeks old, feeding can go down to four hours, but you'll still need to get up during the night. You'll also have to stimulate the kittens to go to the bathroom before and after each meal. And you'll need to weigh them with an ounce scale each day. They should gain 1/2 oz every day. If not, get them in to the vet on emergency.
If you're not up to hand nursing, most vet offices will take them and allow the staff to raise them.
Now, if you decide to allow the mother to give natural birth, you should get her on a kitten food first and foremost. Pregnancy and nursing take a lot of nutrients out of the mama, so she needs the extra fats and so forth that kitten food provides.
A favorite birthing bed is a cardboard box, lined with towels. It should be open at the top, and the sides should be low enough that mama can enter, even with her big belly, but high enough that the kittens can't wander off. The box should be located in the corner or closet of a quiet room. However, you can't force her to have the kittens in the box. She may choose a hamper, on or under your bed, and so on. Either way, add towels to the area, but let the kittens be. Moving them will make the mother nervous and may result in her hiding the kittens. Change the towels as needed, after the birth, and often during nursing, as the kittens' stool may get on the towels.
After the birth of each kitten, the mother should break open the amniotic sacs the kittens are born in and will clear away the fluid from their nose and mouth so the kittens can breathe. The kittens should begin meowing shortly. Most times the mother will begin nursing the kittens immediately, as this helps the labor along so she can deliver the other kittens more quickly. She should also chew the umbilical cord in half, and she may eat the placenta, as it's rich in nutrients. If she doesn't chew the cord off after all the kittens are born, cut it with a pair of disinfected scissors, no closer than one inch to the navel. If the mother doesn't eat the placentas shortly after the whole litter is delivered, throw them out. Most times, cats make excellent mothers, and you don't have to do a thing. However, this kitten of yours is young, and she might need some encouragement. You might have to wipe the babies' mouths and noses off with a clean towel to get them breathing, and then place them a mama's belly to get them nursing.
One thing is critical, you MUST handle the babies daily from birth to make sure they make good pets. The belief that you shouldn't touch young kittens, or their mother might not care for them, is completely false. Make sure you disinfect your hands, and then handle each kitten for a few minutes several times a day. Just don't take them out of mama's sight, or she'll get nervous. Enjoy your babies!