ESH.

SIL was so far in the wrong to even think about doing something like she did. That kind of behavior is absolutely horrible and unjustifiable. The kind of person that would do that has got to be an absolute trainwreck of a person.

But you did punish the child for her mom's actions. The fact of the matter is that you chose to give her the laptop because she needed it; whatever the actions of SIL, the step-niece still needs the computer and her parents can't afford it. And you took the gift back after giving it.

You might be within your right to do so, but I can't agree that this was the best handling of it on your part. You taught your daughter a good lesson of standing up for yourself and others and that people aren't entitled to your generosity, but you also taught a bad lesson that gifts can be taken back after being given and that charity should be conditional. You chose to buy her the laptop because she needed it and wouldn't be able to get one otherwise, but then you changed your mind and took it back. Personally, I think you should have put SIL in her place and later made sure that your daughter knew nothing that SIL said was true privately.

At the very least, the step-niece rightfully views you as the AH because you gave a big gift that was something she needs and then took it away because of something someone else did. You do see how you punished your step-niece for something she had no control over or part in, right?