I have a question about jump height.
Can I run preferred if my dog is 17"?
We really are doing this mostly for fun and I'd rather not have her jump over 12" if I had a choice. The little Corgi mix that beat us in the league injured his ACL the last night we all ran. It's kind of making me a little nervous. I would never want to do that to her.
Honestly, a 12 inch jump height is not unreasonable for a 17 inch dog however, your dog your rules.

so...
CPE doesn't have a Preferred class, that is AKC and in AKC you'd have to jump 12 inches in Preferred. There are no other jump height options in AKC
In CPE a 17 inch dog would jump 16 inches like in AKC
however there are more options for lowering your dog's jump height. CPE has an Enthusiast class which lowers your jump height one below your official measured jump height - or to 12 inches in your case. They also have a Specialist class which lowers your jump height two below your official measured height - or 8 inches in your case.
Just remember your dog will run quite a bit faster at the 8 inch jump height than a 12 inch jump height because there will be no challenge to the jumps - at 17 inches she'll just step over them.
What you may want to consider, even if you opt for 8 inches over 12 inches is learning proper warm up techniques for your dog before you go in and when you come out of the ring. Stretches and other things will help warm up your dogs muscles, much like a human racer, and reduce (not eliminate) injury.
There are a few clubs in California that offer CPE agility,
http://www.k9cpe.com/events.htm. Not sure, given the size of the state, if they are anywhere near you though.