To write from Sheila's point-of-view, consider what she saw and heard. Imagine that you're Sheila and experiencing the story from that position.

At the beginning of the story, for example, you find that the Mant family rents a cabin next to the narrator. They're described as being lively; they're always having parties, playing softball, or going on outings. You could start by recalling the summer as if you're Sheila and remembering spending that time with your family. You might say, "Summer was always my favorite time of year. Every summer, my family went to our cottage on the river, and the warm nights let us spend long hours with our friends in the front yard watching the stars."

Just remember as you write that you're Sheila. Describe your thoughts when the narrator asks you out. Explain why you don't like fishing. Give your impressions of the date. She seems very shallow in the story, but you could give the character more depth by explaining her thoughts and reactions to the things around her.