First you want to be pretty sure that it's not a coincidentally-timed bout of laminitis (if it's 2 or all 4 feet) or an abcess if it's just 1 foot. If it *were* laminitis it would be really important not to brush it off as just a bad trim!
If you are confident it really IS the trim, then unfortunately all you can really do is keep her comfortable til things grow back somewhat. Keep her on SOFT footing as much as possible. This is seriously a big issue if you want to heal things as fast as possible and avoid her popping hoof abcesses (so-called gravel) a month or several months down the road. (edited to add: be careful about the stall rest thing -- with a young horse you can work yourself into much *more* trouble that way, especially if she is not used to lots of stall time, physiologically or psychologically. Personally I don't think I'd do it unless the only place I had for turnout was full o' rocks or was rock-hard lumpy-pointy earth)
If she's really seriously in pain, as opposed to just moving a bit short, if you have bute and feel comfortable giving her 1-2 g per day just to take the edge off the pain a lot of people would do that for a few days. Some people would also have the horse shod for the next cycle, to spare her tootsies, but I have really mixed feelings about doing that to a basically sound healthy young horse unless she was MASSIVELY mis-trimmed, and the farrier really recommended it I would sure want the head guy to be doin' it himself, in your situation.
And the other traditional treatment, which I do find useful sometimes, is to get a can of Venice Turpentine (really ought to use THAT, from a tack shop, not regular ol' paintbrush-cleaning turpentine) and paint that on the soles of her feet, just once (can repeat in 3-4 days if necessary). Keep the venice turpentine away from the coronet and heel bulbs and any raggedy cracks she may have in her frogs. This will toughen up the soles a bit.
To me, one too-short horse-real-sore trim is a bad sign (and I've certainly had it happen occasionally over the years), but I would not necessarily ditch a farrier for that unless I'd been thinking about it anyway (and knew a good alternative to go to). But to me, if it happens again, it's time for a different farrier.
Good luck to both of you!
Pat