I have two 'best' friends - one of a lifetime's duration, one of 14 years. They have been a wonderful support, provider of laughter, a shoulder for terms and a lifeline, particularly In times of need. I love them both dearly, and know if anything happened to me, my daughter would have 2 surrogate mothers. They are quite different in temperament and personality, and that's a good thing also.
How on earth can you stop a child (esp a girl) from having a best friend? Any why on earth would you want to anyway.
I have to add I am also lucky enough to have lots of other friends, colleagues and female family s members. But my 2 BF's mean the world.