actually, standing on blocks is one of the more accurate ways of assessing how much raise is needed, but the high-tech stuff can fine-tune things so that they feel more comfortable and perform better!
As for epiphyseodesis, well don't know what I can say that will make your dd feel better about it. As far as leg length equalisation goes, it is by far the safest and simplest way of getting the difference reduced, and if things go to plan, the legs should end up the same length.
Scarring is minimal (far less than lengthening the short leg), pain is also minimal; as the bone is not broken, as in lengthening, and complications, although they do occur sometimes, are not disastrous.
If she does pull out, it's not the end of the world- if it was done a little later, the amount gained would be less, but possibly still enough to remove the need for raises. If left till maturity, it is still possible to shorten the long leg- but it does involve removing a chunk of bone . That is probably an argument if favour of getting on with it .
How about putting some money aside in a savings account for her to buy a really fantastic pair of shoes or boots when the leg length has evened out?