It is a frameless screen printing stencil. I bought mine from Hobby Lobby but I am sure that most craft stores have them. They were in the stencil section. Ask an associate for them and the printing and fabric inks and squeegee applicators. Regular stencils have open holes and daubers or stencil brushes are used in an up and down motion to apply paint without smearing under the edges. These stencils have sheer fabric in the holes and ink is applied in smearing motion, as she demonstrated. I don't remember the brand name of mine, but I believe the generic term is 'thermofax stencil'. Remember to wash ink out of stencil before it drys in the pores and they last for many projects.
Valerie, I just found your site. I am wondering what type of paint you are using and if you use any type of clear coat when it’s dry. Thank you for the demonstration it is lovely