N/C - Quick background my SIL and I have always been really close. She has 2 dcs, 11 and 14. I have 2 boys 3yrs and 3mths. She has had a really bad year, messy divorce and diagnosed with MS.
Since the birth of ds2 I have found her quite over the top, few examples include taking ds2 off me, unasked, when he was crying saying 'oh auntie x knows how to settle you'; nicknaming ds2 with a personal name to her; regularly saying 'oh well I treat him like he's mine' and 'he feels like he's my baby', 'i'm a second mum to him'. She was so over the top with him at a recent wedding that strangers thought he was her child not mine. I set most of this aside knowing I can be over protective and thinking she was just over zealous and it would calm down, till today...
Both sil and I used to use an equestrian forum as we are both horsey, sil knows I rarely use it now. anyway by off chance I logged in today, it is a small community so when I saw a post started by someone called the nickname my sil gave to ds2 I clicked on it. It had to be her as firstly nickname very unique and all the details matched her life except one, she talked about HER 3month old son. I went back through threads and all the details were there, feeding issues I've had, his weight gain details, a strange rash he had and random stories about what made him giggle, being tired from being up all night etc, etc! But all written as if she is his mother.
I'm seriously freaked out. My instinct is to wrap up my sons and keep them away from her. I don't know whether she just told a lie which went too far and had fun with an online persona (so will feel very foolish that I've seen it) or this is something far more serious. I love my SIL, she's my best friend. What the hell do I do with this?