It would if you anticipated, but it’s way too slow to react to a drill kick with a slide. I instead suggest blocking the first hit and parrying the second, then busting your fastest combo since necro cheaply lands almost right after the second hit (c.short super or s.strong into a juggle).
I think the necro matchup is in elena’s favor; her roundhouse and back roundhouse outprioritize a lot of his shit, though you have to be careful when he has meter because he’ll wait for you to whiff. Make him guess with electric snake and punish with brave dance, use chains and two-hit normals a lot to keep his single parries meaningless and don’t get too impatient since he can anti-air with that ultra-cheap back fierce crap.
The beauty of it all is that she doesn’t have really bad matchups outside of the top-tiers, does decently enough against makoto and not too bad against ken.
Kinda loses to urien, though, because he can keep you out of the air and beat your ground normals… and juggle you easily. My solution is to keep the pressure on after knocking him down by using lots of meaties (to discourage him from doing wakeup headbutts) and EX mallet smash to stay in his face (so he doesn’t space you out with normals or push you into a corner).