Yep, those ripples are due to (probably mild) laminitis - poss what people refer to as 'low grade'. Can't tell if there's anything above the bigger ring of a month or 2 ago, but looks like she's had ongoing, mild problems with it. Diet is SUCH an important factor, and especially as she is now not in work, it will be more so, to keep from feeding too much energy. Re biotin supplement, Biotin is but one of many nutrients that may be deficient/imbalanced in a horse's diet. However, if a horse gets adequate green forage - grass or alfalfa for eg - then it is likely to get enough biotin in it's diet without supplementing. It is apparently quite uncommon for horses to be deficient in it, although this is one nutrient that it doesn't hurt to over supply - excess is just excreted, wasted. Many other nutrients are just as bad to OD on as if they're deficient. Therefore I think a basic diet analysis and a good quality 'complete' supplement that fits your horses situation & diet is a good idea.
Afraid with the angle of the pics, can't really tell any more than the last as far as heel length, balance, etc. A pic sighting down squarely from the back, from heel to toe, along the sole plane would better show the heels, and a side-on solar pic, on a slight angle will better show sole depth & wall length in relation to the sole. Check out; Good Hoof Photos - How to take Good Hoof Photos
And then Keith came out. He said that the bubbly rings and the bell shape are normal, and that the amount of heel we had on her was good. He said that having so much heel after always having so little wouldn't cause her any discomfort. O_o But he said we could start lowering her heel if I wanted, and lower it he did. I'm concerned with how she will handle such a drastic drop, but maybe I'm over-reacting.
Keith is the farrier? Yes, he's unfortunately right that 'bubbly rings and the bell shape' are indeed rather normal. That's not to say they're good though, just that these problems are so common they're often not recognised. As I said, can't really tell from the pics whether there's much too much heel(it's obvious there is some excess & that they're 'underslung' a bit), too much for this stage for her, whatever, but I would guess there's not too much to spare, for now at least. Don't understand where he's coming from as to comments about discomfort & so much/little heel. Also don't understand what you mean by 'normal heel for fronts' comment on the back foot pic? If he thought heel height was good, why did he say he'd start lowering it if you wanted? Again, the angle of the pic may be giving a false impression, but it looks as if he took little, certainly not 'drastic'. I think the main concern is about the strength of her heels/digital cushions, as to whether she'll be comfortable bare with lower heels. If she's not, padding her feet will be a good move for a bit.
As it seems the farrier has rasped just into the sole, this clean hoof shows what's going on a bit clearer(tho it's still just a pic that can be misleading). I've marked your 'after' pic with a line that shows where I think the edge of the sole is likely to be. I suspect the pink & yellow line/area is lamellar wedge. While I wouldn't make a practice of rasping/paring into the sole at all, he may have done this to see where he was - to see 'landmarks' I'm describing, for eg. I would likely(if what it seems is really going on) start the 'mustang roll' from somewhere in the realm of 1/4 to 1.2 inch outside that line, rather than what appears to be just taking the corners off. It also appears, from considering before & after shots, that this farrier may pare frog as a matter of course? I wouldn't advise this, and as with the sole, the frog shouldn't need much if any paring at all, except in the case of paring daggy thrushy bits & perhaps opening up central sulcus if contracted. Paring the frog removes the outer protective layer, as well as thinning it, so causes them to be more sensitive, prone to bruising and thrush.