Yup, I used to do the all the time until I learned to read the stitches. Once I could look at a stitch and know whether I needed to knit or purl it was so hard to try and keep up with my pattern. Eventually I got it though and now I notice a mistake much quicker (most of the time) than when I first started knitting.
I honestly doubt that your mother is going to mind those "mistakes." The shawl is being knit with love that's what counts.