Well the best I think at the moment is audacity. It will record as good as your soundcard can translate. Unfortunatly, there is no 'Protools', 'Cubass', or 'Cakewalk Sonar' for Linux that I know of.
Are you (pre-)amping her mic or are you going directly into the card? If it seems really scratchy it's probably due to the line in setting is set to high. I've noticed when I record my guitar, bass or vocals I have to set the input volume to about 2 (on a scale of 1-10) else it starts to radicaly distort.