Not sure if this is wrong or badly worded, but this is not the first appearance of Lois London, she is the younger sister of Dazzler and first appeared in that series. This might be the first time she got a super-alias though.
Mortis (Character) - Comic Vine (gamespot.com)
Hi, I looked into this. What I was able to find is a 1st cameo in #20 (Which has now been added), 2nd cameo in #21, 3rd cameo in #22 and 1st full in #23. She does eventually get her superhero alias Mortis in X Necrosha which would be her 1st app. as Mortis which is why it noted there