4 year old overly clingy with friendships

[Thumbelini]

Looking for advice / recommendations. 4 year old DD is very clingy when it comes to friendships. In any setting she instantly zeroes in on one friend and decides they are her best friend even if they aren't really that interested and sometimes not even that kind to her. Tried multiple ways of encouraging her to speak to or play with other children but it doesn't seem to get through. I feel heartbroken for her but I'm out of ideas of how to teach her how to make friends or how to not get so obsessed with one person. I'm also wondering about an attachment disorder? Any book ideas or advice would be most welcome

My DD is like this! I hope she will grow out of it, is she an only child? Mine is so I'm not sure if this makes a difference or not.

My DS can be like this...not as extreme but he is very much focussed on a "best friend". He's also four.

He seems to have grown up a bit in this area but he started reception this month so it'll be interesting to see if he's actually playing with different children other than his "best friend" from his nursery class.

What makes you worry about an attachment disorder, is your DD adopted?