If she needs a big SUV because she tows horseboxes across muddy fields, for example, fair enough. It may be an uncomfortable truth, but truth it is - if you buy a big heavy car "to feel safe" what you're doing is buying a big heavy car "to come off better than the other party in an accident". Theres a given amount of energy to be dissipated in a crash, by crumpling body work and throwing vehicles and their occupants around etc. If you (a) increase that amount by having a big car, and (b) make the other vehicle, by virtue of weight disparity, undergo a disproportionate amount of crumpling and acceleration then you really are buying your safety at the expense of theirs.
As you say - sometimes our freedoms need curbed for the good of us all.