THE most affordable professional sound recording and mixing software is Cool Edit Pro. There is a freeware version of it, but it has use limitataions and a short expiration date. For personal use, it's only $100 bucks or so...maybe even cheaper now. It's a professional package that comes with every sound modification (echo, auditorium, flange, etc.) you can humanly think of. It's in use in just about 80% of radio stations in the US.
Sadie (with AudioVault) is far more expensive and has a far steeper learning curve. SoundForge is pretty good, kind of in between the two.
Remember that raw sound files and songs take up a large amount of computer space, so have plenty of Gigs of storage on hand or get one of those 254G external storage drives.
When ever she is done with a song (project), back it up on the external drive AND burn it to disk, label and catalog it in a safe place. I have seen talents go into a RAGE when a project was lost, damaged, or a computer crashed and it was all lost--hours of work down the drain in an instant.
Good luck! If there is anything I can do to help let me know!
ROX