If I wanted my hypothetical SO to avoid another lesbian, especially one she had never been sexually or romantically involved with, then that would be a sign of insecurity and immaturity on my part. If my response to that feeling is to try to find ways to stop my hypothetical SO from interacting with their friend because I don't like them, that would cross the line into relationship abuse, in my view. It's one thing if I don't want to interact with the friend or don't care for them myself, but trying to control the interactions that don't involve me is not healthy relationship behavior.
And yes, I'm not sure if commenters are men or what, but lesbians are also friends with each other in addition to dating each other. Often the friend group is primarily LGBT/lesbian, rather than being composed primarily of straight women and men. There's not special standards based on the friend or coworkers orientation, nor are lesbians relating it to typical dynamics between heterosexual men and women.
Now, circling back, I don't think my insecurity leading to me wanting my hypothetical SO to not interact with someone is relationship abuse in and of itself. However, I am obligated to engage with that feeling directly by, for example, seeking reassurance or communicating what behaviors toward me help me feel secure in the relationship (eg, in my case regularly spending time together in person where I receive that person's attention means I can be less insecure the rest of the time). If I want this to go well, I should also phrase it in a calm and nonaccusatory way where my partner is doing me a favor to help me feel better, rather than that they did something wrong. That way, when they make the change, they can feel good about doing so rather than bad.
I'm speaking more generally because I already discussed the dynamics of this story to death on dynastyscans, which anyone can feel free to go read my comments there. This comment is not myself trying to "take a side" with Mashiro or Makino within this story. Clearly they have a lot to talk about and there are compromises they can make to both get what they want, without dictating the other person's behavior.