From the systems I’ve studied—Buddhism, Taoism, and Hinduism—they all talk about reincarnation, and there’s a shared saying:

Dying while protecting one’s child is one of the greatest stores of good karma.
Buddhism speaks of “protecting others by sacrificing oneself, offering one’s body to feed the tiger” as the conduct of a Bodhisattva. What this dog mother did is, in essence, exactly the same as the story in Buddhist scriptures about sacrificing one’s body to feed the tiger—knowing she can’t escape, yet choosing to stay and stand in front of her children.
Taoism speaks of “hidden virtue” (yin de): accumulating the deepest merit through good deeds that seek no return and remain unknown. She doesn’t know what karma is, and doesn’t know what reincarnation is—but she has done everything that those teachings describe.
If reincarnation is real, then in the next life this soul will not be any worse. The universe will not shortchange a soul like this. No matter what the mechanism of reincarnation is, if one can manage not to give up even until death, then the next leg of the journey will not be worse.
It’s already the worst it could be—after this, it can only get better.