I don't know if I would go so far as to call it resentment. From what we saw early on, Menma's mother is suffering from grief rather badly. Menma's father and brother have moved on a bit, but her mother hasn't really. She performs an offering and prays every day.
As I said earlier, I think she's only upset because Menma's friends only care now. They didn't visit Menma's home back then (because they were afraid of Menma's father), and worse, they spent all their time chasing Jinta's mother. They didn't even come to visit Memna's memorial after she died. Now they come back and make everything raw again. From her point of view, it may make them look callous. It may look like they're doing it out of something they want, and not so much for Menma. Menma's dead, so how could it possibly help or mean anything to her now?
As she said at the end of the episode, it seems like a joke.