Substance abuse?

I have an aunt like this. I suspect mental illness combined with boredom. She stopped working when her first child was born and still hasn't gone back to work even though both children graduated college several years ago.
She will reinvent the past, pit one family member against another and accuse people of treating her unfairly. She will stop speaking to a family member for several years and then resume the relationship as if nothing happened.
What does your husband say? Is this something he's seen happen before?
I would have DH call your FIL just let him know that SIL sent a letter. I wouldn't engage with SIL directly.

She could be in the early stages of dementia.

You wouldn't know unless you spend time around her. It sounds like she's kept to herself for a reason. My sister is very good at hiding her condition because she knows it has upset people at work and in the family when she has told them her "truths" in the past. Most people have no idea and the doctors have been fooled into thinking she is just depressed because she is articulate and feigns normalcy so well. But every few weeks, I will get a strange email or message telling me about some incident that I need to attend to or worry about regarding my family, especially my parents.

Anonymous wrote:For those of you who say mental illness, what sort of mental illness? This really hadn't occurred to us as a reason. Thanks!

My sister developed paranoid schizophrenia in her twenties. We knew something was wrong when she started telling us about things we knew didn't happen. She would be adamant that they did and become very angry when her memories were challenged. Had anyone spent time around her and checked out her living environment? Has she let her personal appearance and home deteriorate? All these could be indications of mental illness.

Anonymous wrote:

Anonymous wrote:Isn't she sort of old to be developing some of those? She's in her early 40's.

I will say this: I've known her for almost 20 years and in those 20 years she's had one romantic relationship we've been aware of (it lasted about 6 months). But this doesn't mean there haven't been some, she's very silent about herself, we know very little about her aside from the fact she works, where she lives, etc.

Then maybe something else is going on. Regardless, this isn't something you should obsess and push about.

I'm not -- I doubt I will ever have a conversation with her about it. I doubt I even see her in the next year.

Anonymous wrote:Isn't she sort of old to be developing some of those? She's in her early 40's.

I will say this: I've known her for almost 20 years and in those 20 years she's had one romantic relationship we've been aware of (it lasted about 6 months). But this doesn't mean there haven't been some, she's very silent about herself, we know very little about her aside from the fact she works, where she lives, etc.

Then maybe something else is going on. Regardless, this isn't something you should obsess and push about.

Isn't she sort of old to be developing some of those? She's in her early 40's.

I will say this: I've known her for almost 20 years and in those 20 years she's had one romantic relationship we've been aware of (it lasted about 6 months). But this doesn't mean there haven't been some, she's very silent about herself, we know very little about her aside from the fact she works, where she lives, etc.

Anonymous wrote:For those of you who say mental illness, what sort of mental illness? This really hadn't occurred to us as a reason. Thanks!

People who I know who've sent these kinds of notes have personality disorders and are desperate for attention and thrive on others' misery/trouble so they can feel better about themselves.