Whatever her policy limits are. There will be a ton of investigation done, and it can get quite complicated. However, given the fatalities involved even if they could reduce liability to any degree, it's still worth more than what her policy limits are. However, this case is likely to drag out for years. The school district is going to be brought into it, the municipality, potentially the manufacturer of the lights/bus, the families' insurance carrier potentially (for underinsured motorist). I obviously don't know who her insurance is or what her limits are, but if they're smart, they'll offer them up immediately.