I just made a post today about her.
I personally don't know if this would be the best way to go about fixing her, but I think this would be one way to at least approach it.
I think the Oathsworn portion of her passive should be moved to an ability so that it works much like Taric's Bastion, including offering some sort of active effect that she benefits from by casting it on herself with no allies nearby to be her Oathsworn.
This would also remove the limitation of having a single Oathsworn throughout the entire match. I do like that idea, but I think it could still be health without it.
Also, this would mean that they could get rid of The Black Spear
. It's honestly unnecessary. It's an item that triggers an animation then goes away. That is literally all that it does. An ability could accomplish the exact same thing, and would offer greater flexibility.
Now that we have moved Oathsworn to an ability, we have too many abilities. I think moving Rend to her passive would actually be better.
Instead of making Rend an active ability, she will automatically rend all spears after landing her 5th spear in any target, including spears placed by her Q. This would decrease the potential strength of stacking a massive amount of spears into the same target, but it would allow for greater up front damage and damage amplification for less spears on a single target.
To clarify, If you were to attack a single target 5 times, on the 5th spear, all 5 spears would be rend from that target for massive damage.
If you were to attack 5 different targets once each, on the 5th spear all 5 spears would be rend for minimum bonus damage.
If you were to attack 3 targets with 3, 1, and 1 spear(s) respectively. The first target will receive an amplified bonus damage, while the other two will receive minimum bonus damage.
I do understand that this would cause some pretty substantial balance changes that would need to be considered as far as damage, and resource costs are concerned, but I think it could offer a positive impact on her gameplay.