May I offer unsolicited advice?? Starch the fabric well before you cut!! Use smaller cuts, like fat quarters, if you are wanting a scrappy look. Ask me how I know about the starch part. Kathy

Yes as Kathy J says, starch is important as you will be working with bias edges which will easily stretch out of shape. Also handle the pieces carefully as you sew them, taking care not to pull on them or tug them out of shape.

With or without starch, handling the pieces like newborn babies is key to success in this quilt!

Not sure if this will help -- is your grandmother in a wheelchair, by any chance? I sew wheelchair quilts for charity; it is recommended that these quilts should be smaller than other lapquilts, so they don't get stuck in the wheels. The recommended size is around 36 x 44, or thereabouts. (I just made a wheelchair quilt that measures 40 inches square.) Otherwise, I make lapquilts larger -- the size above (54 x 62 inches) sounds right. Also, I agree with starching. I didn't realize how important it is not to stretch bias edges when I started; starching and careful handling are very important!

You probably know that you must also consider fabric requirements for binding and backing.

I had this link in my bank of goodies. It is a very pretty equilateral triangle quilt pattern/tutorial:
https://sewfreshquilts.blogspot.com/...-tutorial.html

Thank you for the advice about starch! I just received my fabric and am about to start preparing everything. Will make sure to keep everything starched and work carefully with my cut triangles :) Will let you know how it turns out!

One thing I learned from using 60° triangles...I start by putting 2 together at a time, then joining sets of 2 together. That didn't work so well, it was hard to match everything up. It was much better joining them 1 at a time to the strip. Agree that starch will be your friend.