An exclamative sentence where the main clause begins with que expresses a wish or an order.

Que la Force soit avec toi ! (May the Force be with you! — G. Lucas)
Que l’on apporte un os pour ce petit chien ! (Bring a bone for this little dog! — Gosciny)

It’s fairly old-fashioned. Nobody would use it to give an order these days, and it isn’t used much to express a wish either.

“Qu’il(s)/elle(s) crève(nt) !” is a set phrase that is still common in modern French even though the general construction has become uncommon. When it is applied to a person, crever means die (this is informal French only). Thus “Qu’elle crève !” literally means ”I wish she’d die“. It’s actually a bit of a hyperbole: it really means “I don’t care about her, I don’t even care if she dies, I’m not going to expend any effort on her behalf”.

To add to Gilles answer, IMHO it’s more slang than Modern French. There is also a pejorative and belittling sense to it.

“Crever”, when it means to die, means (to me) to die from a disgraceful death, one that no one cares about and one that will not have any meaning.

COMPLÉMENT

The question of the nature of the verb “crever” as raised by Brucher is apparently of sufficient interest but I thought certain corrections should be brought to that answer, as well as I deemed worth considering other ideas.

The word is not reckoned with as slang by the TLFi, but I would say that there is a slangy feel to this word. It carries no connotations of belittling, however: there are numerous people using this word in refering to their own death and they nevertheless have a good opinion of themselves; neither self-criticism nor self-deprecation can be at the root of this usage; what you find as a connotation is the feeling of helplessness of the human being facing death, the evocation of a vain and last struggle, more particularly as perceived as an end in throes, in the agony of pains due to disease, without the alleviating effect of medical care and even without the amenities due by family and religion or possibly without the confort of a death bed.

Parce que je n’aurai songé qu’à moi, qu’à moi seul, (…) il faudra que tout un pays périsse! Il faudra qu’une pauvre femme crève à l’hôpital! Qu’une pauvre petite fille crève sur le pavé! Comme des chiens! Ah! Mais c’est abominable!
HUGO, Les Misérables, t. 1, 1862, p. 283.

This perception of death is the opposite of what others prefer to consider apriori as a peaceful death; the word is considered as pejorative in the TLFi; however I think it does not merely stress a negative aspect of a concept, that concept remaining essentially the same, but it adds something to it and as such deserves another definition; it’s not just saying “dying is bad”; instead of calling “crever” a perfect synonym of “mourir” it should be defined as “mourir de façon très déplaisante” (to die vilely).