Im guessing one of the friends texted "what was that comment"
That actually makes a lot of sense! It's probably Kumako then. Though sadly I still think it'll most likely be college related. We can hope though! (T^T)
I have been wondering if these were flags or not: here, here, and here. And whether they were related.
Am curious if we were going to get the 'going to different schools' story arc for a while now, but it's just a guess.
Whatever the actual context of the text, it's pretty clear that the "friends find out" and "leaving high school" issues are closely related--the series has been pretty methodical about signaling the passage of time (unlike some "in high school for eternity" manga series), and the reveal to the friends has been the Sword of Damocles development hanging over the series since (checks notes) Chapter 1, page 10. In other words, these are the key developments that have been in the cards all along (well, that and them actually having sex, but I don't expect that's what the text was about).
This situation is ripe for the "studious Chidori goes to university, feckless Nanoha goes to vocational school" resolution, or, in the alternative, Nanoha figures out that the thing she wants to do requires college as well.
I just don't want the "previously unseen relative wants Chidori to live far away for her last year of high school" trope. Do we even know why only-child Chidori lives with her grandma? Are her parents alive and absent, or gone permanently?