Cast of characters
MIL - an unbelievably generous person (possibly to a fault)
SIL - 19 YO with a history as the "problem child" (lying, stealing, massive financial irresponsibility etc.); She joined the military this year and now lives out of state (she lived with either MIL or FIL up until then.)
SIL came to visit the family for the holidays, making it the first time we've seen her in almost a year. She'd seemed to have really gotten her act together and shaped up. All that changed after a day or so.
It became clear that the real reason SIL decided to visit was that she wanted the spare car she had been allowed to use when she used to live with MIL. DH and I told MIL it was a bad idea (SIL got in a wreck with the same car a year ago. She had been pocketing the money MIL gave her for insurance and did $10K worth of damage to the other driver's BMW. MIL ended up bailing her out). MIL was charmed by SIL's "changed" ways, and agreed to give her the car after they got it inspected together. Well, it turns out the car needed a lot of work done...$3k worth of stuff. SIL said she had no money, so MIL paid for it although she could barely afford it. She even called DH and I and apologetically asked us not to cash the check she gave us for Christmas until her next paycheck cleared because she had to spend the money on the car. We said okay. So obviously she made a big sacrifice.
MIL paid the bill and told SIL that she'd consider $1k of it a loan that she'd have to be repaid since it was really out of her budget. Rather than being thankful that she was only asking for a fraction of it to be repaid, SIL blew up at MIL. She yelled at her for not helping her out, accusing her of being a bad mother, etc. She packed her bag in a hurry, and stormed out the door, yelling that she was going to hitchhike to FIL's house an hour away. She blocked all our cell phone numbers so we couldn't call her. DH went looking for her to no avail. We were worried sick.
Well, several hours later, I was on facebook and I noticed SIL had posted some things. I was relieved she was okay until I read what she wrote. She posted that MIL had called her a [bad name for a promiscuous woman] among other things (lies) and that she had thrown her out of the house for no reason. She also said she'd hitchhiked back to FIL's because we refused to let her in and told her leave. Several people had already responded that her family was horrible, she deserved better, etc.
DH and I were so angry at her outright lies, that we commented on her posts. I said, "You forgot to mention the part where MIL paid $3k to fix the car she was going to give you for FREE so you could have your own vehicle. Yes she sounds like the worst mother ever."
The next day, we saw SIL had deleted our comment. We're livid that she'd spread such toxic lies about MIL, who is such a selfless person. We're probably going to give her the direct cut, but how do we handle these lies she's spreading? Should we message family members and family friends who are on FB and make sure they know these are lies or just stay out of it? MIL does not have FB and she's not great with English, so she isn't really able to defend herself that well.