I have always been surprised that in BFME in general and a lot of its mods, Shelob is particularly underestimated in terms of power.
There are 2 things that in my opinion would justify a bit of change about how she works :
-the first, Shelob doesn't serve anyonelse than herself. To invoke her alongside the forces of Mordor doesn(t quite fit the lore.
-the second is about her actual strenght. While there is a parallel drawn between Morgoth and Ungoliant in terms of power, There is also that between Sauron and Shelob. Here in the Two Towers : "So they both lived, delighting in their own devices, and feared no assault, nor wrath, nor ay end of their wickedness" (Shelob's lair chapter)
In terms of pure, harsh power of evil, there is a match. The difference is that one of these evil can spread, whereas the other is condemned to be consumed in the shadows.
With that in mind, Shelob would almost deserve tp be a tier 4 power. However that is not my suggestion. My suggestion is this one :
-Interverting the Reinforcment of Rhûn and Shelob in the spellbook to integrate Shelob in the defensive tree that suit her best, even if the Reinforcment from Rhûn are permanent.
The spell could be put only close to a main base of the player, a castle or a camp. The first time it is used, it would create a building which would be untargetable, and undestructible by anyone : Torech Ungol, Shelob's Lair.
This lair once appeared could not change location during the game.
Once it appears of the first time, Shelob would immediately come out of it but should be not controllable. She would instead attack any ennemy units within its range which would be quite good. She would have more speed, more attack speed also to be the impressive beast she ought to be, and of course a very high armor and a lot of hit points.
However, she would be on a short timer and after that time is finished, she come back to her lair.
The lair of Shelob also would have a cooldown button. After the cooldown is completed, Shelob would come out of her lair as soon as ennemies are wihtin her range of attack.
She also could be drawn of her lair by re-using the spell from the spellbook on the lair even if there is no ennemies within range, but that will also reset the cooldown of the lair.
The lair wiould get experience from nearby kills. The more victims who go within Shelob's borders, the less hungry she is and the more darkness she weaves.
Levelling the lair from level 1 to level 5 would reduce at each level the cooldown of the lair, allowing her to spawn more regularly.
If Shelob once spawn has no more ennemies within her range, she would stay motionless, unless allies come too close (but at far shorter range than ennemies) in case she wiould also attack allied units. But she would change target as soon as ennemies come back within her range, feeling a far more delicate flesh to feast upon.
Even if Shelob would be on a timer each time she come out of her lair, she would also have an health bar, and she would retain each time she spawns the health bar she had at the end of her last sortie, without being able to regain health by any way.
When she eventually dies, she could not be revived and the spell from the spellbook would be far less powerful. it would be able to be put on all the map and not just on Torech Ungol but would only spawn a standard broodmother.
I don't know if it is technically possible, but I liked sharing this suggestion.