Skull Watch has a 10 hour duration. Assuming there are limited mountain passes for the PC's to approach from, she should have plenty of warning that the PC's are coming. That will use up some of her L3 spells, though. Chain of Eyes is a divine spell anyway, and could be replaced (or she could use that instead of Skull Watch to keep an eye on aproaches, especially if she has a familiar). Resist Energy could also be replaced, but seems a good spell for a defensive wizard, and Invisibility and Alter Self make sense, although the latter won't help her much at present. I'd ditch Spirit Worm in favour of Grease (or a different L1 spell that doesn't require getting into melee range). You could swap Dispel Magic for Fly, or Dispel any magical augmentations they may have.
I expect she should have 40 HD of Undead under her control. Tireless guards who can pull ropes to release traps on the trail to the cave? Animated creatures, rather than just human/orc Skeletons and Zombies? If nothing else, fallen orcs become reinforcements. Tiny Skeletal mice/birds would have no combat utility, but provide a different approach to an early warning system (which could free a 3rd spell slot for something more combat-worthy rather than Skull Watch).
If you keep Chain of Eyes, with Dandu's suggestion re the familiar, she can use Skull Watch as an alarm, send the familiar out to scout (Invisibly, if desired), then slip down (or Teleport down) to their campsite to leave them with less/no supplies (and possibly some dead huntsmen). Could she also prevent the spellcasters getting a decent night's sleep?
Slipping into their campsite to Contagion sleeping adventurers (repeatedly) also has some appeal, but even though Invisibility may get her past the guards, the need for verbal components screw stealth up, and unless she can find cover for the castings, she'll be visible after the first one. If she can get that sheler, and cast off a host of spells, that Spirit Worm could be a lot more devestating, but while I can see someone not waking up on taking ill, that one seems likely to wake up a sleeping target.
I'm surprised there were less than a few thousand able-bodied orcs in the whole campaign world (there's less than 400 left here; is/was the other clan that much larger?). Especially if they're desperate, it seems likely the females and older children (and orcs have short childhoods) would be armed as well. It seems unlikely a shy, retiring Orc of either gender or any age would last long.
I'm confused by the situation, though. The Orcs don't trust the sorceress, but they still followed her up the mountain to the caves, only days after their defeat, while she was licking her wounds? Or is this where the tribe had already retreated to (within days after their defeat?) and now she has rejoined them (and they let her?)
And if you want to add a few more spells, she could have gained enough xp in that failed campaign to level up (one new spell of each of L 2 - 5 would add some options).
A lot depends on how you want to play her out - desolate and scattered, or "After all I have lost, they chase me to even this poor excuse for a refuge? No, for this affront they will die!" A Scrying (chain of eyes), Teleporter with Fireball spells (or animating all those dead orcs, if the party chooses to slaughter the women and children) seems like a nasty enemy if she turns to guerrilla tactics...
