Cinderella has got to be the most well-known fairytale in the world. It is also incredibly old and has thousands of variations...That being said, there is no way that I can possibly do full justice to the rich and fascinating history of this tale type. But I'll do my best to give a suitable overview of the Grimm version.
The fact that the woman who willingly marries the widowed father was most likely doing so because she literally had no other options--due to poverty, age, or suspected infertility--is never considered because her feelings are of little value. The potential for being resentful at having a husband and children forced upon her for reasons out of her control is is great, but it doesn't matter, given that women are expected to be motherly, no matter the situation.
This story came to the brothers by way of Wilhelm Grimm's future wife, Dortchen Wild. It is believed that Charles Perrault's The Fairies was a source of inspiration, given that similar punishment/reward systems were used for the kind and unkind girls. Some variants have the queen asking the king that mercy be shown to her stepmother and stepsister, who are then banished instead of executed.