I was this child too, my parents put a lot of energy into facilitating friendship-making opportunities including brownies and other hobby groups...but that just gave me more places to be friendless unfortunately.
In my case the problem was me, I couldn't just naturally pick up social skills, and being repeatedly thrown at groups of children my age didn't cure that! I could knock along happily with others, but not convert it to meaningful relationships, and all my friends had their own groups of friends that I was not in. It was very lonely.
I truly wish the problem had been picked up on earlier, my parents either didn't realise it was me, or thought it would hurt my confidence to suggest I was doing something wrong. I think they tried to protect me by telling me I just wasn't meeting the right people. Eventually as a young adult I spent a lot of time researching friendship making psychology, and now have excellent friendships in my life and am much more confident socially.
Can you observe her with other children? Its unlikely its just a hobby issue, plenty of children have diverse friends, and it's not like the most popular people have the most popular hobbies, the most popular people can make a friend and find a connection with almost anybody. This is an incredibly wonderful life skill and can be learned.
There are books that exist for all age groups that teach specific social skills. They also have the advantage of showing that this is a common problem that many people need help with and nothing to be ashamed of. Its no different to needing extra help with maths or sports or anything else.
Here's one, Amazon have loads
www.amazon.co.uk/dp/0963815210/?coliid=I1ET905VK724L0&colid=24ZVNQQRGCWM3&psc=0&ref_=lv_ov_lig_dp_it