First we took a rectangular piece of material about 8-9 inches long by 5 inches wide. If the pattern of your fabric runs a specific direction, make sure to cut your fabric accordingly. Mine was a scrap but ended up having a cute butterfly we were able to place right on the front. Fold it in half (short end to short end) with right sides facing. Press with iron.
here on how to box the bottom. I will say I think she adds a few too many steps. I don't use a regular ruler to measure in where to sew. I use one of my quilting square rulers. Line up one line up the seam you've already created, then draw off your line at the bottom to show you where to sew. Her version of this in the video occurs about 1:13 minutes in. With the size of this bag, you will only need to measure in about 1/2 an inch. There is an alternate way to box the bottom of a bag here.
When you have all your edges ironed inward, pin the strap to ready for sewing.
Before attaching the strap, fold in the top edge of the bag about 1/4 of an inch and press with the iron.
Place the straps inside the bag about 1/4 inch down and lined up with the side seams. Pin.
Sew a seam around the top edge of the bag. If you have a small arm on your machine, you may be able to fit it around, but I was not. It takes some maneuvering to make sure you don't sew the front to the back of the bag.
When I normally make purses, I do much more to hide open edges, but since this was just a basic bag for a doll it will suffice as is.
I'd also like to thank her for her help with the photography of this post!