The parts aren't that expensive but I'd let her try the downtube shifters first. It's a very personal choice. I have bar ends on one road bike and dislike them because I find it hard to shift the front der with my small hands. You don't get any more accurate or fast shifting with barcons over downtube and the cable is even longer so you may sacrifice some performance.

http://www.sheldonbrown.com/harris/s...s.html#barcons

Unless you can do the labor yourself, you'd need to factor in the cost of an LBS doing the work.

Switching to STI could be exorbitantly expensive as you'd have to replace the dérailleurs and maybe even the cassette as the number of speeds comes into place. With friction, you can mix and match stuff a bit more.