I have an 8 month old pitbull and a 9 year old male. She is

Usually if the dogs do it themselves a litter results as they know more than we do about it.
While there is a 'morning after' shot for dogs it lengthens the heat season and may predispose a dog to a uterine infection.
The only other way around this is to spay her within the next 3-4 weeks.
If you decide to go through with the litter you need to keep her nutrition levels up so that hopefully some of the food fed will go into her and not just into the puppies she is carrying.
A 9 year old male certainly is very likely to be fertile particularly if he has been stimulated by her heat season.
Hope this helps you!

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Will having a litter at this young age cause problems for her in the future with growing to her full potential or even when she has the litter. If I do decide to do the shot the uterine infection can be treated if worse case. Will the shot prevent her from having any other litters in the future? I wanted to breed her but it was one of those take your eyes off for a second situations.

Do you know what the name of the medicine that is used for the shot?

It might impact her growth to full mature level as the way it works is everything gets put into pups.
So swapping her back on a good quality puppy food and perhaps adding a daily vitamin mineral supplement would be a good idea
This site talks about mismate shots and other medical means of terminating a pregnancy in a dog
http://www.veterinarypartner.com/Content.plx?P=A&A=1564&S=1&SourceID=42
and this one too
http://www.dogchannel.com/dog/breeds/breeding/article_13295.aspx
Prostaglandins would now be the treatment of choice to abort.
If she got an infection from the shot the usual 'treatment' is spaying to save the dog's life.
Personally I'd go through with the pregnancy as the safest course and make sure mom got top notch nutrition and that I supported lactation by supplementing mom with goats milk and started pups on solid foods including goats milk as a supplement to mom's milk at about 3-4 weeks.
The only way I've found that works to keep two intact dogs apart is complete separation such as secure crates or kennel runs and never having both dogs loose at the same time.

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