Don't know that i agree with the bars comment, but agree otherwise to what Kimmy says above, sorry.
Now from just those few pics, there is a lot that is left to be assumed & guessed at, so my comments on what I see may or may not be accurate...
Firstly, it appears that the farrier has carved off an awful lot of frog unnecessarily, which will cause the horse to be more sensitive & reluctant to use his heels(think of someone cutting away the calloused layers of your sole & only leaving a little soft skin). As a rule, I don't think paring frog is a good idea, unless it's daggy or thrushy bits that are best removed. Apart from possibly opening up the central sulcii a bit more &/or treating there for thrush, it appeared your horse's frogs didn't need any trimming at all in the last pics. The red circles on the back of the frogs are where I'd be concerned about possible infection.
In the back pics the red outlined area at the toes I'm concerned with, because it seems the farrier has possibly rasped/pared into the sole? I would almost invariably not touch that area & it usually can do with being a lot thicker, not thinned further. That goes for the fronts too, if they've been pruned. Looks like the farrier has possible pared a fair bit of sole all round, which I wouldn't tend to do. *Again, not assuming, just telling what looks likely.
The black lines I've marked at the toes are approximately where I'd start a strong bevel/roll to releive the stretching. The black line at the inside quarter of the back left indicates where it appears it could be imbalanced & needs attention. *Again, can't really tell from this angle, so that's a guesstimate. It appears the right back may also be a little higher on the inside. *This imbalance may or may not be right for this horse too.
The red circled areas at the outside heel of back right and the inside heels of fronts indicate where it appears the heels could have been left a little long, forward & out of balance with the other side of the foot. Looks like the inside front bars could possibly be addressed further too.
This horse hasn't got very 'underslung' feet at all - poss left fore only one that I'd really class as that now, though he has got stretched toes still, which appear that they're possibly not being addressed well.
I don't get what your farrier means by working on thickening heels or the widest point of the foot moving back - excepting quarter flares that can change the *appearance*, the WPOF should remain the same. Check out Equine Lameness Prevention Organization
for more info on that point. While depending on many factors, it can take some time to effect many real changes in a foot, I also don't understand why it should take (another) 6 months for her to make that happen, considering the horse didn't look like it had much of a problem at all 6 months ago. Is it possible she's stringing you on, telling you what she thinks you'll believe? Not saying she doesn't believe it herself...
Anyway, sorry for what must be a dampener for you, & could well be wrong, but I think it's well worth considering all those sorts of aspects and that perhaps a better trimmer is in order?