
I'm sorry to hear about your girl.
your vet should be able to tell you how the healing is likely to take, with a puppy the healing is usually quicker. You will probably need to return to the vets for some further xrays in 8 or so weeks to check the bone has started to heal.
Also, if she has not had surgery the healing might take longer as the bone can move, really depends on how badly her pelvis is broken. I assume it is not broken very badly and the bones are still on correct position as I would think the vet would have not left it to heal on it's own otherwise. Sasha's pelvis had moved so we had no choice but operate and also due to her size she needed the legs to line as well as possible. I believe smaller dogs and cats cope just fine with wonkier pelvises and are often left to heal without operating.
In our case it was 12 weeks crate rest and then slowly building her back up. It is very important to keep the dog as still as possible so crate is needed to keep them calm and you need to stop her falling over as well as she could damage herself further by doing so. Sasha was in the crate 24 hours a day only taken out to do her business. She had to be half carried from her waist as well, to minimise the pressure put on her healing pelvis - This was done for first 6 weeks if I remember right and then slowly easing out the support and letting her put more weight on the leg. If your girl is smaller breed she might not need this much support, Sasha is a Leonberger and weights 50kg so lot of weight was going to be put on the plate if she was allowed to walk unaided.
Sasha had her accident in mid November and it was summer time she was allowed off lead exercise again but this was largely because of her size and we did not want her to damage anything due to lack of muscles so had to take it slowly. Sasha has recovered very well and I remember the vet telling us the damage looks nasty but pelvis fractures often heal very well and dogs can live perfectly happy "normal" life once they have healed. This is why we went ahead and I have to say we are delighted and would have never believed how well she did heal! If I did not tell you, you would not not know the major trauma she went through.
There is a section on her accident on our website with some pictures of the xrays and little more detail of her recovery period.