If all that embroidery is to be done by machine, you/she'd be better off to do the embroidery before you sew up the kilt, and especially if the bottom of the kilt is to be hemmed. I'd recommend sewing a liner over the entire embroidered apron (not just up at the waist) to protect the inside of the embroidery.
I used to work in a screen printing-embroidery shop and have learned these kinds of things the hard way.
I like the idea, and am looking forward to seeing it completed. All she'll need then are some black hose with orange flames worked into them.
Hmmm......