The sword isn't as great as you think. Let's delve into some science here.

First, the sword has far greater size, but equal mass to her bastard sword, meaning that leverage applied to the base (Where someone would strike to disarm you) has a far greater effect than a sword of equal size and relative weight, or even of her original sword's size and weight. So in fact the very property that allows her to wield it easily makes it easier to knock out of her hand (Let's say the equivilent of knocking a normal sword out of a normal person's hand.)

Second, the striking bonus only applies to blows, meaning the sword must have full momentum for the multiplier to take effect. If she misses, which is all too likely when facing an opponent with high AGI, someone can easily trap the sword by simply stepping on it, and she'd have to rely on her own unmodified, albeit still considerable strength.

Thirdly, even with her strength and the multiplier, it is unlikely that she would be able to easily swing the sword with impunity wherever she is. Underground, in buildings, or even in a dense forest, the sheer amount of material she would have to cut through to swing the blade would slow it down until the modifier was no longer active, making it an effective way to lose her weapon.