The SKS is muzzle-heavy, no doubt. I keep a basic web sling on mine. I carry muzzle down, and don't completely remove my left arm when I shoulder the rifle. I just rotate the sling around to the back of my upper arm, just above the elbow. With the sling adjusted to the right length, it pulls tight when I shoulder the rifle and allows me to brace it with my left arm, supporting the forward end in a very stable firing hold. Someone here might actually be able to supply a picture or instruction diagram to illustrate.
Good luck, and I hope y'all find a solution that works for her.
- TS