@Cable_TV
Abe was first mentioned back in chapter 11. Right after Nanoha and Chidori started going out, their friends ran in and told them that they saw Abe asking out Yoshida. Personally, I think this is when Chidori and Nanoha decided they had to keep their relationship a secret
no matter what, since their poor little hearts couldn't bear the embarrassment of having their friends find out.
Abe and Yoshida have shown up very briefly since then in a few of the little in-between chapter sketches the author throws in, and they're seen once in one of the volume extras (Chapter 24.5), but other than that it's basically been 80 chapters since they appeared in the manga, and even then it was a brief mention on a single panel.
As kind of irritating as this situation is, I'm really happy to see Abe and learn more about her. I actually thought this whole situation was really funny, like the author is deliberately messing with the audience.