My sister got married this fall. When my MIL heard she was engaged, she started dropping hints that she wanted to be invited to the wedding. We ignored them. My sister was having to cut people from the invite list anyway. Plus, they've met once and I thought it was strange she would expect to be invited. And oh yeah, not really my place to be requesting my sister invite certain people to her wedding.
MIL sent her a gift anyway. We took it with us.
The day we got home from the wedding, MIL asked if they got the gift. Then every wee or so she would ask H if he was sure. "Because I haven't heard anything about it. Did they like it?" In other words, my sister hadn't sent her a thank you note yet.
Today my MIL got a thank you note in the mail from my sister. She called H. "Did you tell her I said something? I find it odd it just showed up out of the blue."
OMG. No pleasing her. And of course we never said anything to my sister. It just took her awhile to send notes.
Your sister should have had her thank yous out in under a month; this is late. That said, your MIL is a complete nut job.
I agree she should have gotten them out sooner. However, I don't think it was my business to tell her so. So, I certainly was not going to ask when MIL would get hers.