I'd do the epsom salts or ACV soak, as chlorine might be a tad too drying, but either way you want to do it, it fine.Just don't soak too frequently if you choose to do it again later..the softer hoof will be more sensitive and other parts of the wall will be more apt to break.
The way that looks..it looks like in front of the missing chunk it extends a little just below the coronary band, but still has some intact wall right below? That's what it looks like in the pic, and that might come off later as well.
For now, in the abscence of any real pain or sign of infection, just leave it be, try to keep it as clean as possible for a little while (Yeah, right, I know, that's tough to do with a horse. LOL) If you do get worried about junk getting in there, you could make a duct tape wrap , or put a boot on, for while you are working her but mostly, just leave it be. You can soak it every few days as a preventative for that gap, but the broken part is exposed to air, so I doubt you'll see any infection develop there, and once that last bit of wall comes off, it won't cause any more worries.
She might occasionally have take a sore step until the heel has grown back a little better, just because it's lacking the natural protection,and hitting rock just right could sting, but it isn't likely to be much of a problem, esp a horse that isn't being ridden yet. Time, turnout, your usual good care and observation, and she'll be fine. It's kind of like if you ever rip your nail back into the quick, and trim it, but that last piece rips off really short.It can sting at first, but your finger looses the sensitivity and it grows back as usual.
Thanks for sharing the pics..I'm such a nerd, I like to look at every hoof people are willing to show me, esp with things like this! Plus, someone else may be browsing that have a similar issue and this helps dispell any concerns!