Regardless of the stripes is she eating like a healthy fish should? My Red Betta had stress stripes for around 3 days when first introduced. In fact during my cup observation on purchase she looked the least healthy to begin with but I liked her coloring and took a chance.
The first several days I was worried. Out of the 5, she was the one who always remained hidden in the corner by the plants. Anytime any of the 4 decided to challenge her she remained passive and swam off. The only food she was able to scrape up were ones floating to the bottom near her.
Fast forward today, I guess getting quality foods and proper water maintenace improved her outlook and health as she has quickly become one of my most active females who is no longer afraid to push others aside for food.