Turns out the 18" dolls have a torso length that's quite similar, so the shirt fits quite well. The legs on the Dollfie Dream, however, are significantly longer. It turned the knee-high pants to shorts. They did, however, fit and the people around the world rejoiced.
Springfield also makes shoes. Dollfie Dream feet are about 7 cm. long. I was able to take these sneakers, which admittedly are not as cool as some of the Dollfie Dream specific shoes I've seen, and slip them on just fine.
For under $15 total, I was able to give Rally a full new outfit. Very pleased! I may have to pick up some other clothes in the near future, as long as I'm okay with all the new pants being shorts.
Link: Springfield Clothes on Amazon.com