Good evening, this is not for me, but for SIL, who is not a mumsnetter, but is trying to seek advice.
SIL's MIL (for ease, I'll initial her just as "A") has a young daughter of 11, along with BIL, who is much older. A went on a holiday abroad last month for three weeks, leaving the daughter at SIL and BIL's house. She is a difficult child, and spent the time she was staying with them screaming (actual screaming) for more time on the iPad at bedtime, for the cats to be taken away from her, not wanting to get up for school, lots of strange behaviour. She was also texting her mum saying she was being mistreated, called names, etc.
Upon returning home from her holiday, A picked up her daughter with no thanks, and no word from them for a fortnight. Then, out of the blue two nights ago, she starts texting SIL late in the evening (we were out for a meal) demanding to know why her daughter had been mistreated, etc- she hadn't been at all. When SIL responded that she didn't wish to speak with her, and that she could talk to her son when he finished work, A sent a stream of very nasty text messages calling SIL delusional and a bitch, and saying that she would "come and get" answers out of her as to why she didn't want to speak to her. Some of the comments were extremely personal, such as accusing SIL of wanting to leave her husband, that she hated her mum, and that she had "flushed her first child down a toilet" (SIL had an abortion at 18). SIL refused to engage, and went to bed.
SIL and BIL have two small children, A being their paternal grandmother. Today she has sent a very formal text to both parents stating that they need to arrange regular visitation with her for the children, and that SIL and BIL need to respond within 7 days or she will get legal advice.
SIL is extremely shaken, and is considering calling 101 for advice- what can be done from here? AIBU to think she can't just suddenly start demanding visitation after no other communication than a stream of abusive messages?!