You'd have to see the overall dimensions of the poodle in question. I would not judge by weight ever. Rather, if both are in good shape and the pieces to the puzzle fit, you should be fine! Also, before breeding her please, please, be sure to have her tested for everything physical (heart/eyes/teeth/hips/knees/elbows/liver) and be sure that she herself does not posess any congenital defects that she is likely to pass onto her pups or be affected by during pregnancy!
Best of luck to you and yours. While I understand your reasoning, I myself would not cross breed...still doesn't mean that I don't want you making educated decisions! Have fun w/ the new girl!
Post photos when you get a chance! I'd love to see her.
ps. In regards to her having issues w/ whelping the pups due to her weight, don't worry, look at her size first. Also the body structure at birth for both poodles and yorkies are quite similar (give them an hour to fill out and form and there's a big difference, but not till then) and so you shouldn't have any problems on that end. It's the initial mating that you should be more concerned w/ structurally.