RIP Poor cat.

Does this lady show remorse about her RBcat ? You don't say..

As you can't stop her getting a second cat, I personally would go on damage control.

Can you re-educate her on the proper care of her cat (without shouting at her)

Suggest a good vet, which send out yearly reminder cards.

Post about the affects of diseases on cats / dangers for badly inoculated cats.

I can't think of anything else.

Fingers crossed that she has learnt her lesson (at the expense of her first cat) and treats the next cat properly.

PS. Maybe alert the local RSPCA shelter if she 'forgets' about the new cats shots.