Sadly, I understand Yukino. It is a strong possessiveness that comes from lacking experience, being overly dependent, and having abandonment issues and obsession with the past (both hers and others'). This combination makes the mind a monster, creating stories that aren't real and obsessing over facts that can never be changed while poisoning itself repeatedly. It is extremely unhealthy and borderline impossible to overcome without some major self reflection and efforts. It doesn't help that some of her most important development time was spent chasing her dreams as an idol rather than interacting with society and those in it.
As someone that struggled with this for years, I can safely say that any relationship she has before tackling these issues will almost certainly be doomed.
I understand she's bitter that she had to let go of her dreams while Mika got to realize hers, but to say she wasn't happy that Mika contacted her again, that she wishes she didn't encourage her...
The issue here is that, as of this point, it seems more like Mika is contacting Yuki because of Nao coming back as an AV and more or less causing issues because of their past. I mean if her intentions were anything else, then she would have contacted Yuki about her solo debut without a flimsy excuse like losing her number. If she wanted to contact her, Mika could have contacted their old agency for her unchanged contact info.