How old is she?
Many factors to consider on the algorithm used by insurance companies
1) Somebody involved in an accident is more likely to be involved in another
2) I assume large personal injury claim
Might not have been her fault but could she have done more to avoid the accident? Did she not see the car approaching the roundabout at speed, Wrongly assuming he would stop?
What I'm saying is a very competent driver never assumes anything for granted and most of the time when I'm driving I assume somebody will do the most retarded thing possible and it's surprising how often it happens, For example: Somebody in the left lane on a round about and they turn right, (no indicator) Whilst I'm in the right hand lane going straight on. I have assumed the tard will go right and yep 3/10 times it happens, But I've backed off expecting it letting them continue, yes I could have gone straight on letting them crash into the side of me but I see it and avoid so I don't get shunted. Insurance claim avoided.
Somebody with the record of a PI claim and involved in an RTA would be considered more high risk to insure than somebody who has been accident free for 2/3/4/5years etc...?
Regardless of fault
Statistically (and insurance is all about statistics) Spmebody involved in an accident is more likely to be involved in another.
They will pay but you have to claim on your own policy. I crash down the road and say o shit I got side swiped by an uninsured driver, Get a fault free claim everytime, Never going to happen.
Insurance is overpriced. But it's over priced because parasites bleed the system dry, Ambulance chasers/accident management companies/hire cars/workshops/lawyers/barristers/courts all overcharging for services provided.
https://www.moneysupermarket.com/car-insurance/why-is-car-insurance-expensive
explains it all nicely
pleass don't take this as a dig at your sister, I'm just using it as an example and have no idea of the facts of the case, But that is why she is less "attractive" to insure