I'm surprised they wouldn't give you an option for an ultrasound, but how far along is she? I will be going in for an x-ray just weeks before she delivers; it's too early to do that now as the pups haven't developed their bones, therefore, an x-ray wouldn't be able to detect anything if it's too early. So that explains why they couldn't x-ray, but as far as an ultrasound goes, my vet told me they could do that for me. As far as palpatations, I don't know of many vets who do that. Any acutally...I didn't think that was a good thing to do. I could be wrong, but depending on how early she is, that might not do anything for her (they wouldn't feel anything either).
Let me also add that you want to have an x-ray done close to the time she delivers anyway; so yes, I'd recommend waiting so that you can clearly see how many puppies to expect and whether or not one or more of her puppies may be too large (and possibly cause complications during delivery).