I think she was probably doing what I've always known as 'Twist Rib', it's firm, very stretchy and it looks great on cricket sweaters in particular.ecando said:
It is indeed based on a K2, P2 rib but the K2 is a mock cable: insert the right-hand needle into the front of the second stitch on the left-hand needle and knit it, then insert the needle into the first stich, knit that and slide both stitches off the left-hand needle together thus creating a single cable.
It can be done on every row, which creates a very tight rib band; only on one side, the right side RS (odd numbered) rows; or over four rows with the twists on rows three and four, rows one and two being a simple K2, P2.
The last is my personal favourite, but knit up a test swatch and see which you like best. If you don't get on with knitting shirring elastic in with cotton yarn, this will retain its shape better than a standard rib.
Hope that helps.
Dave