Yeah, 2 lumps of coal won’t be hanging around for long up there… 
If she’s on a 70mph motorway overtaking a lorry that’s limited to 56 at the most, she wouldn’t have taken long to get past, so I must admit that it sounds to as though she wasn’t ‘doing the speed limit or slightly over.’ On the other hand, why potentially be the cause of what could have been a right old smash up by tailgating.