Size 7 in shoes for boys is equivalent to a size 8.5 for women's shoes.
When shopping for shoes, it is important to note the differences in sizing between men's/boys' and women's/girls' shoes. The biggest difference is that men's/boys' shoe sizes correspond to a larger size for women's/girls' shoes. Therefore, a size 7 (youth) in men's/boys' shoes would correspond to a size 8.5 in women's/girls' shoes.
To get the right fit, it’s best to make sure you measure your foot properly before making the purchase. You can also check out this comprehensive guide on women's shoe sizing: https://www.liveabout.com/womens-shoe-sizing-4072742. It explains in detail how women's shoe sizes are measured, and how to convert them to other countries' sizing systems, such as UK and European sizing.
Good luck shopping for shoes!