I think they're keeping Niki/Jessica's power deliberately vague. In particular, it's unclear whether she had the power to absorb a personality, and along with it a superpower, or whether she's just got super-strength all the time, but has the dual-personality crutch preventing it from always manifesting. In the future-show, we saw that the dual personality was gone, but we didn't learn whether the super-strength was gone as well. One can imagine that this aspect of Niki/Jessica will be a big deal at some point, if not in the season finale, then later on.