Other driver is claiming serious injuries but her IG tells a totally different story??

Three things your parents need to do today: (1) call their insurance company and report the demand letter, (2) screenshot every post you found and back them up somewhere permanent like email or cloud storage, (3) stop talking about this case on social media themselves. That last one is more important than people realize.

I don't want to be harsh but I'd be a little careful about assuming the posts tell the whole story. Some injuries genuinely are intermittent — someone with a real back injury can have good days and bad days. That said, the posts you're describing sound pretty active, so definitely bring it to the insurer and let the professionals sort out what's legitimate. Just don't go in assuming fraud out loud before anyone's evaluated the medical records.

From a medical standpoint, soft tissue injuries from low-speed impacts are real and I'd never dismiss them entirely — but the functional limitations she's claiming would typically show up on clinical exams and imaging. If she pursues this legally, she'll have to produce medical records, and those records either back up her story or they don't. The social media activity you're describing would be pretty relevant context for any doctor or jury evaluating how impaired she actually is.

Ugh I'm so sorry your family is going through this. Your sister already feels bad about the accident even though it was minor — and now having to deal with something that feels so unfair on top of that has to be exhausting. Hopefully the insurance company takes this seriously and your family doesn't have to carry this stress for too long.

A few practical things: your parents should notify their insurance company immediately if they haven't already — they have a duty to cooperate under the policy. The insurer will assign a defense attorney at no cost to your family if this goes to litigation, so your parents probably don't need to hire someone separately yet. That said, if the demand is significantly above the policy limits, that changes things and they might want a consultation just for themselves. Also — save those posts somewhere offline, not just screenshots on a phone.

I worked in claims for years and yes, social media is absolutely something defense investigators look at — and so do plaintiff attorneys on the other side, honestly. Screenshot and save everything with timestamps right now before she makes her profiles private. Don't engage with her accounts, don't like anything, just document quietly. Insurance companies do fight inflated claims, especially when there's evidence like this. Your parents' insurer has a Special Investigations Unit (SIU) for exactly this kind of situation.

Don't assume the insurance company is automatically on your family's side here. Their priority is closing the claim cheaply, which sometimes means settling even on a questionable case. Push them to actually investigate. Ask specifically whether they're doing any activity surveillance or social media review. You may have to advocate loudly to get them to use the evidence you're handing them.