How useful do I think she is? She’s ok. Most of the time, you’re better off just picking Woody.
Just how much power do I think she gives? A lot. A LOT. For example, lvl 125/O7 Jack Sparrow’s “Avast” will do 20k per shot. With Judy + 1 support, he will do 28k. With 2 supports, he will do 36k per shot! For every Support she has with her, she’s bestowing 9000+ Basic Damage for everyone, but it really all depends on how the battle unfolds. This kind of power is only available for the first 7 seconds after activating “Deputize”, is only available again for an even shorter 3 seconds whenever someone KO’s an enemy, and a measly 2 seconds after she revives AND maybe still has allies left to take advantage of it.
What I’m saying is, because this power is only available in occasional short bursts throughout the fight, it’s no wonder we won’t notice it all the time because that power is not actually there all the time.