Does she just want it just for her lap? Or to come up to her shoulders?
Not everyone's idea of a lap quilt is the same.
When I make a true lap quilt, I measure across the person's width and add approx 12" to each side. Then from their waist to the floor and add 12" for tucking under their feet.
For a larger one, I measure from their chin to the floor and add 16" or more. I measure the same across their middle and add 12". I want them to be able to tuck it all around themselves :D:D:D