I hope she's using really thin yarn, if not, that's one reason it's tight. For learning, get her some really large needles, size 10, it will help her see the sts easier, and using worsted weight yarn they won't be so tight.
There's a knitting article on how to loosen up, though I don't have a link for it. But one reason seems to be that after making a st, people tend to pull on the yarn. Watch to see if she's doing that; making the next st will tighten up the previous one. Also make sure she's not holding either the needles or the yarn with a death grip. New knitters tend to do that, thinking that if they hold them loose, they'll drop a stitch. Even if they do, they can be shown how to put it back on the needles.