Thanks for the question.
Catholics hold the remains of the faithful to be sacred, as they once were temples of the Holy Spirit, and an integral part of the human person to whom they belonged. (They are also a sign of our hope in the Resurrection of the body). So generally, the remains are buried, or in the case of cremains, they are put into a sacred repository, which are in many cemeteries.
While the practice of dividing relics has long been part of the Catholic tradition (generally with the approval of a Bishop from a known saint), still dividing of ashes has not. I don't think that this practice would be in keeping with the intent to keep the remains in a sacred place of honor, because if you think about it, it wouldn't take much for some of those remains to find their way into some unfortunate place. Ultimately, the Church would not approve of it.
I would suggest that you talk with your sister about an alternative means of giving everyone a part of her: photograph collections, heirlooms, etc.
Keep the remains in a common place, a repository at a cemetery would be best.