In fashion, what is the protocol if my tailor hemmed my pants too short?Ugh, the "tailor blew it" issue....and you probably can't buy a replacement pair!
The protocol is they should offer to make it right; that is, let the hem out longer.
How much longer do you need them? How much of an inseam did she leave?
If there is enough fabric in the inseam to make the pants long enough, she can add length by interfacing the hem with another fabric. She can let out the pants to the maximum length and sew on fabric, making that the inner part of the hem. I usually ask to use a stiffer or heavier fabric so the pants weigh nicely at the bottom, unless they are a moveable fabric, like silk or crepe.
If there isn't enough fabric in the inseam and she saved what she cut off, she can add this back and make your pants into cuffed pants. It's relatively easy to do, though it completely changes the look and line of the pant.
If neither of these are acceptable solutions, the tailor needs to refund to you the cost of the pants.