If you starch the fabric heavily, then handle the cut pieces gently, the method she uses will work. I know several quilters who use this method exclusively and have no problems.
Personally, I have problems with this method, so I cut 2 squares an inch larger than the FINISHED size of the HST, put right sides together, draw a diagonal and sew 1/4" on each side of the line, then cut on the line. Press, then trim the resultant triangle to the correct size. Since you sew on the diagonal (bias) it is stablized and your HST edges are all on the straight of grain.
Everyone is different, there are lots of methods for creating a HST. Try them all, then pick the one that works best for you.
There are lots of nifty HST rulers out there! Don't know which one you got, so can't advise on its use.