I'm very sorry to read this happened. Don't like, don't comment, that should be the policy.

You should definitely not delete the comment. Let others see what a nasty and ridiculous person she is. But I also think it's wrong to share this on Tumblr for a laugh. That she might even see as justification of her comment. 

Supreme indifference and no reply is the best policy imo. Even though I realise that can cut deep and hurt tremendously. However, the person who commented is obviously in the wrong. Best to ignore her and not feed her ego.