Ellena didn't stop, despite consuming tremendous stamina from that huge attack, she dashed towards the monster to finish it off.
Magic attacks won't suffice. It would just mar the surface, and Ellena couldn't create another strong magic in the meantime.
There was plenty of energy from the lightning. I am certain that she used a huge chunk of her stamina just to produce it.
Conceivably she noticed that it could withstand some numbing but was not completely lightning-proof.
Well, lightning is electrical energy, and mostly, monsters that have water in their bodies are conductive too.
This monster is just an ordinary monster. Hence, it can only resist some normal paralyzing attacks. It doesn't possess any ability to be precise. If there was, I would firmly make Ellena plan well before going.
Or I will plan well first before going. Maybe some traps would suffice if this monster possessed some ability.