Medjed being a 40% element/10% resist eidolon is a viable event eidolon for the main slot. Also, her stats are good enough such that if you ever pull Nidhoggr in the future and need thunder eidolons in the sub slots, you'll be fine picking Medjed as one of them.

Medjed gun has Pride (S) on it as well; that comes out to +7% assault at lv 20. Less than optimal, but you're still getting offense out of it at least while you're mainly equipping it for the HP.