TBL is knitting 'through back loop'. So instead of inserting the needle from the front of the stitch to knit it, you insert the needle through the back of the stitch and knit it that way. Doing so twists the stitch. There is a video demonstrating this on the following page. It is listed as ktbl:
Actually, now that I look at it I see that SKP is also shown as a video demonstration on the same page.
Good luck to your mother! If she gets stuck with any other terms, you are likely to find all explanations here!