Well, this is kind of insensitive. I think that all dogs are different, and it’s going to be really hard to tell whether you will be able to achieve penetration with any dog before she is grown just going based on breed.
With all that said, I have looked into this myself, as I am raising a lab, and am hopeful that sex will be possible for us when she is ready. It may not be, depending on a couple of factors, one being, the size of penis you/me are working with, and how receptive the bitch is, and whether she is of a physical size large enough to take it. So, if you have something the size of a table leg between your legs, then there’s no hope getting it into any dog. If you have any measure of normality down there, then a larger breed should (theoretically) be able to take you.
I am concerned that you can’t fit in a Dalmatian, as I believed them to be of the medium/large dogs, so I’m guessing you’re either gigantic, or perhaps your girl isn’t as receptive as she could be? Are you trying when she is in heat? Are you employing various forms of foreplay to get her going?