Sabrina is pulling a I'm-going-to-contract Madoka on Homura. Except that it's worse.
What is Sabrina to her? Someone who knows what she's gone through, as well as her best chance of taking down Walpurgisnacht. Best chance ever, a chance that probably isn't coming again.
What is Sabrina doing? Constantly putting herself at risk, for the sake of others. Said others include helping random magical girls from other cities, and
Oriko.
Spreading around the information that you'll Grief Clean anyone, which is pretty much waiting for Tokyo girls to get a hunting group to lock Sabrina in a basement and use as a Grief Dispenser. Because being willing to help everyone for free, while running around, is not as good as 'locked in our basement'.
Currently, dealing with a random MG that doesn't trust Sabrina, and normally always turns into a witch...
All of these obviously are risks that Homura considers unnecessary. From her view? It doesn't matter how well-meaning and useful Oriko is, Sabrina as she is,
is already enough for Walpurgisnacht.
Sabrina's feather-threat-justification of keeping Orika around, to Homura, probably looks like an excuse. Regardless of whether that threat is real or not, it must remind her of Madoka's "I'll throw myself away to save others".
The main reason she's silently putting up with it so far, is because she had crap luck on her own, and Sabrina isn't giving her a choice.
Homura has only one priority, while Sabrina's goals are same as Madoka's, to save everyone/break the system. In that regard, she can't help but doubt Sabrina's decision making/priorities in regards to saving Madoka.
I don't really see any immediate ways to fix that impression; but, Homura will stay put anyway/hold herself together, because she doesn't have much of a choice.
Stress that Madoka is #1 on Sabrina's priority list,
and act on it. As little unnecessary risks as possible given Sabrina's character. Can focus on her messiah complex/feathers/what else after Walpurgisnacht is over with. That'll help calming down Mami, too.
Of course, with things happening lately such as Sayaka mysteriously getting transported, there might be a lot of interference in the future, even before Walpurgisnacht...in that case, that interference would be a good way to go about convincing Homura of reality of other threats; once the mystery has been solved, or Oriko has been somehow excluded from being behind what's happening.
As it is now, I don't really see Sabrina convincing Homura of anything, as her decision and perception must look compromised to permanently-paranoid-PTSD'd Homura - as if Sabrina has come to a conclusion about Oriko already, and is interpreting what's happening only as to try and justify that conclusion.
Satisfying her paranoia somewhat, and gathering more facts, before bringing up feathers with her, could be useful. Giving her even more control over Oriko, or something along those lines...
Mentioning a feather that you found in a barrier is probably good, as that's a fact(and Sabrina wouldn't just make that up)...without trying to interpret it, letting Homura draw her own conclusions.
Going for feathers-behind-what-happened-to-Sayaka is way too early. From Homura's POV, Oriko could be behind it just as well.
Well, at least that's my impression
I could be misreading the situation completely, or reading it worse than it is.
Homura was willing to give Sabrina benefit of the doubt back when she kept Oriko alive, and I'n not sure if I'm interpreting correctly her reaction to things that happened since(Sabrina did put herself at risk more, but she also saved a lot of people...they aren't named Madoka, though).
She does look more insecure and less pleased with the situation, to me.
