Careless Driving charge from at-fault collision

Hi everyone. I haven't been here in a while. I hope everyone has been doing as well as possible during the pandemic. My wife was in an at-fault collision last week. It was snowing and she was driving about 20 km/h. Approaching a light, she braked. She hit some slush or ice, the ABS kicked in and she hit the back of a school bus. No one was injured; there was minor damage to the school bus and there was the expected amount of damage to her car. She totally accepts that the insurance company has deemed her to be at fault. Because a school bus was involved, police were called. My wife and the bus driver had already exchanged insurance information before the officer arrived, but he collected it all again anyway. He then charged my wife with careless driving, saying he "has" to when she's at fault. I've seen many comments here that that's a judgment call but that some officers insist there must be a charge. The insurance implications from the collision will be minimal. We'll simply lose our no-claims discount. But the careless charge is another story. If I'm not mistaken, careless is a serious offence for insurance purposes. My wife has a nearly impeccable record from 40 years of driving, but insurance companies don't care about that anymore. Beating a careless charge will be difficult. Even though the officer wasn't there, he'll testify that it was snowing and that my wife should have been driving even more slowly, leaving even more room, etc., etc., etc. I'm sure she did everything correctly for the conditions, but we know what winter driving can bring. What would you say the chances are that a prosecutor would offer a reduced charge of Follow Too Closely at an Early Resolution meeting/phone call/Zoom? I believe that charge is a minor offence for insurance. If that's major, what else could we try to get that would be minor?