I think it's great that she's 'just a pet'. Her being a pet doesn't necessarily have to affect your altering decisions, though. My questions to you are:
1. Can you handle the MESS of going through a heat cycle with your dog? It's messy, it STINKS (why does no one mention the *smell*?), and be prepared to shampoo your carpets and go through a box or two of pads. Chlorophyll helps.
2. Can you keep her contained during a heat cycle, and for about a week after? That means on a leash, supervised in a securely fenced in yard, crated, and at least 2 doors in between her and any intact males at all times.
3. Did your breeder want her left intact?
If your answers to either of those are no, please go ahead and alter her ASAP - before her first heat. The world doesn't need any more unwanted puppies, especially from an bitch that's way too young and probably not health tested. There's no clear-cut, right or wrong answer about when to alter your pets, but we can all agree that we don't need any more poorly-bred or mixed-breed Dobermans.
If you answer yes to all of the above, then you can definitely choose to leave her intact for a heat cycle or two. The benefits:
-Less chance of inverted vulva/recurring UTIs (my neighbor is dealing with this with her bitch)
-0 chance of unwanted puppies
-less mess and fuss
-can prevent the occurrence of certain cancers
-according to some studies, can increase lifespan in large breed dogs (if left intact until 4 - I think this was the golden retriever and rottweiler study)
-lowers the risk of growth plates staying open too long, leading to orthopedic issues
-*can* lower the risk of leaky bladders
The cons of leaving her intact:
-dealing with heats
-the risk of pyometra
-increased risk of certain cancers
-convincing your vets this is a good idea (most are pro-spay)
-having people lecture you for leaving your girl intact like it's their personal crusade to alter every pet they see.
It's up to you, or it's between you and your breeder. My personal vote is to leave them intact as long as possible, but that's only if you're willing to prevent unwanted litters. If you're not, or you don't think you can, I would vote to spay ASAP.
As far as the differences between an ovariectomy and an ovariohysterectomy, it's up to you and your vet. Lots of US vets will do either procedure. My vet is very pro-oavariectomies. She says it's a smaller incision, less bleeding, less risk to the dog, less time under anesthesia, etc. She said that in her experience, bitches have fewer "leaky bladder" issues after it, but not all vets agree on that. It's a common misconception that there's a risk of uterine infection and cancers if you only remove the ovaries, but the uterus actually atrophies and disappears on its own. As far as I've been able to find, there are no studies proving that there's more long-term risk with an ovariectomy.
This article is by a vet from Belgium who is currently in PA on his experiences with both procedures. Two Ways of Spaying a Dog: Ovariohysterectomy vs. Ovariectomy