Anna made a big deal about not confusing E2's sexuality with his gender identity, but yet she is doing the same by referring to her gay friend as "sister". What does Matt's sexual orientation have to do with his gender identity? She is always mis gendering others.
As for her prior friendships with lj popsey, Sabrina, and Amaaya, as well as Bing and a few of the school mums, those friendships probably didn't last because those women are busy working and living life outside the home. Her new bestie probably has all the time in the world for her if he is a stay at home parent like her. I also think it can bring up a lot of insecurities for her if she sees these other women doing so much more than her, it makes her feel crap about herself. Instead of using that as motivation to do more, she probably ghosts them or stops reciprocating and putting effort into the friendship. That gushy post is very odd, it definitely is stunted teenage behaviour, as are many of her other behaviours and things she says and does.