Do you think this is disrespectful or are they blowing it out of proportion?

Yes it is ridiculous. Extremely so. But don't down play the role she takes in your lives, although she pays nothing she also is paid nothing so to me it evens out the score on that front. This has turned into one of those things that isn't really about a Wendy's combo. I'm going to give you a valuable piece of advice here, let it go and make peace. Just be the bigger person and sit down and ask her to forgive you for your thoughtlessness. Are you going to mean it, NO WAY, but sometimes in life we suck it up and play nice to keep the peace. Next time you go, don't tell her you went and don't get her anything if you don't want to because you are right you shouldn't be under any obligation to not only provide her with meals at home but provide her with meals out to. What she doesn't know won't hurt her. She sounds petty and unreasonable, am I right? But your not going to win by playing petty and unreasonable with a pro so change the game on her and be sweet, apologetic and sincere. That way if she keeps up the grudge then she will be the one who is definitely wrong!