Her feet will improve with time, but it might be worth going to a foot specialist because her feet really shouldn't be sore with that amount of dancing.
You could also try these soft insoles (made of spongy rubber or gel-type material)in some practice shoes. Forget this "must be right on the floor with the soles" business unless you're championship-grade dancers.
Supadance make excellent practice shoes, but your partner will still need the inserts for comfort.