Agree mostly with what others have said. We need more pics to get much of an idea, but it's obvious the horse has been suffering ongoing lami for some time & the walls(esp evident inside quarter of white one) are disconnected from a long way up. The cracks are a symptom of this, as well as(based on this pic being taken just after a trim) poor trimming.
First & foremost, if she's been lame since she was shod, I'd get the shoes off her pronto - preferably last week
. It is most likely farrier error that has caused it, so have a word to your farrier & ask him what he thinks may have caused it. Might be a genuine accident, such as a nail prick or some such, or it may be he's one of those who pares sole &/or frog or some such, in which case it's an error of method & I'd definitely look elsewhere.
Secondly, as others have said, good diet & nutrition are vital, and if this horse has been suffering lami on grass alone, I'd be restricting her grazing - muzzle her or keep her on a bare lot, eaten down area, 'paddock paradise' track, and feed her hay. I would also definitely avoid feeding grain, molasses or other sugary/starchy 'junk food'. Whether this 'farriers formula' stuff is right for her or not, she will also be lacking & imbalanced in a range of nutrients, so yes, a *good quality* complete supplement or grain-free 'ration balancer' will be good for her. They don't actually get much out of a mineral block(& they're often bound together with molasses, so bad news), and a good supp should give her what's required.
Thirdly, educate yourself as much as you can on the principles & factors which effect feet. Farriery is but one small part of it and most of the responsibility is down to you. But if you don't know what comprises a good trim, then you'll need to learn in order to gauge the proficiency or otherwise of your 'expert' of choice too. hoofrehab.com barehoofcare.com & safergrass.org are some good resources to begin with.
I would not be getting this horse shod at least until her hooves have become healthy & strong. Or for that matter, at least until she is mature, so her feet have a chance to develop fully before they're restricted. I'm not against shoes in any situation, but I believe they are generally unhelpful at best when applied to sick feet. Hoof boots or such are generally better alternative when she requires extra protection for her feet.
I wouldn't bother paining anything onto her feet, as someone already mentioned, it's pretty much useless, except perhaps to make her feet look a bit nicer.