How to keep curls intact?

Okay my sister has real straight, semi-thick hair. It is a little longer than her shoulders and is layered. It will not hold curl good, but she doesn't want a perm. She washes her hair and then puts moose in it then rolls it with sponge rollers while it's still damp and leaves them in for about 7 hours, then she lets it down and hairsprays it, but the curls only last about half a day. How can they last longer? Please don't suggest curling irons or hot rollers because they won't curl her hair either. ThanksHow to keep curls intact?
instead of using rollers when wet, try getting a set of hot rollers. before putting them in use a pre- heat spray like biolage. follow the instuctions they come with, and after spray with a super hold hairsprayHow to keep curls intact?
One word, Electric boogaloo
i have fine DEAD straight hair, and the only thing that works for me for 12 hours is... wash my hair, semi blow dry it, then hairspray each hair stand before i put on my hot rollers... then i'll leave the hot rollers in over night, or at least 6 hours before what ever i need my hair to be curly for.... then i'll take them out and hair spray it again..... and the curls stay intact.... i don't use those hairsprays that give you white residue..... i use sally's stuff... you should be able to get that at any sally's