Sorry, I overlooked this thread earlier, as I've had mucho experience fighting feedback, and may have a suggestion or two. First, there's no indication of what kind of guitar she's using, and that's a crucial part of the equation. A Gibson J-45 will be much less prone to feedback than a Martin D model. Generally the copies of these styles will react like the originals. My main working guitar is a Lowden copy of a Gibson J 50 (I know, it's a VERY early Lowden) The guitar (unlike it's Gibson counterpart is exceptionally loud and bright, but resists feedback well when miked at the 14th fret, with the mike at a 45 degree angle. It took me a year with a lot of on-the-job experimenting to settle on this placement. The old 0-18 I now use can be miked straight into the hole with no feedback problems. A good approach is to call up an experienced ACOUSTIC music sound person, and ask what they have to say about the general set up they'd use on your make of guitar. I've found they love to talk shop.