Tragic, but she would have known the cost of the vet bills - if she couldn't afford to pay maybe it would have been better to put the foal to sleep quicker?
Depends on the situation i.e. is it safe to stop or would it endanger horse, rider and pedestrian? I try and be as abiding as possible with other road users. I detest the view that horse riders are snobs and ignorant so try and combat this by being amenable if appropriate.