I don't think this woman deliberately overstepped. She has never been a mother and so was unprepared for the pleading, etc., that kids can do when they want something. Hopefully now she has learned her lesson though.

I don't think she was trying to buy love so much as just being a nice person.

It's not her job to manage the relationship between her husband's ex and his daughters. It's her responsibility to be a decent human being.

That means she should treat her stepkids with kindness and get a better grip on boundaries - for example, if, in future, the step daughter sees a wedding dress she wants to buy, step mom should certainly say "no, you need to buy that with your mom" and make it stick!

But if the daughters are angry with their father, for example, it's not step-mom's responsibility to step in and try to fix things. That is for the father and his children to work out.