The liquid starch bottle you see in the picture is just a concentrate of starch that you can dilute down and put in your own spray bottle. I use it all the time. You can do all of the above tricks with it, but I just dilute it down to what ever strength I want---usually 3 or 4 parts water to 1 part starch. Doesn't matter what the portion is-- 1 cup, a cap full, or a glass you happen to grab. Of course you can use it straight out of the bottle, but then you would be cutting a pretty stiff piece of fabric LOL! When you spray and iron right away you can get the white flakes if the starch isn't soaked into the fabric and it can stick up the bottom of you iron. I just spray and iron-to lazy to wait
.... The more starch on the fabric the stiffer it will be.
She is using it to help with the edges and give you a crisp fabric to work with. You do not have to use it if you don't want to. I use starch because the fabric is easier to handle and if you have a bias edge it doesn't stretch out as much with handling.
Good luck to on your new project!