You and I see this the same way. Classic manipulation, especially since she called her friend a bridezilla. Truthfully, mom should know that her autistic child cannot attend. It would really be a poor decision; terrible for the kid, her, and the bride and groom. The bride needs to keep her spine, and if this means she loses a friend, so be it. The friend thinks that the wedding is her big day.
The sympathy for the mother is that she never asked for the situation of having an autistic child. And she didn’t take a way out. She’s staying a mother. But she must often be at her wits end and looking for outside help to give her relief. But her sense of empathy is totally lacking if she expects relief for her at the cost of her friend’s potentially ruined wedding. It probably means she’s not a good friend and not a big loss.