When I was cheated on I wanted to believe him too
I think, personally, if I were your friend I would find it helpful to hear your perspective and hear from you that you went through the same reactions and feelings I was going through.
Presumably she is aware of the final outcome in your situation, so you wouldn't need to labour that point, you could just share the reeling do you went through. The denial, trying to believe anything else possible, etc.
Not to convince her, but to give her the opportunity to open up without feeling embarrassed - if it were me I'd find it helpful to be given the opportunity to say "me too" without having to feel foolish for trying to convince myself of the opposite of what my instincts were saying. Then if she wants to ask you more specifics, or whatever, she can do so without you feeling you've pressured her.
I wouldn't tell her what to do, but if she asks your opinion I'm not sure hiding it from her to sit on the fence is helpful either. But just frame it in a way where you're not telling her what you think she should do, you're just telling her how you interpret it. E.g. Saying "I don't believe story, it sounds implausible because x y z" without adding "and therefore I think you should leave".
Telling her that in your view he's following the script, isn't the same as telling her what to do about it. E.g.:
F: do you think she really is crazy?
You: well, it sounds like a bit of a convenient story to me, I've heard it before, but what do you think about it?
Or something that sounds like you!
Sow seeds, rather than instruct, if you know what I mean?
Try not to let the fact you wish he hadn't hurt her like this, and the fact you want a happy ending for her, cloud what you tell her or mean you don't give her the opportunity to think through what it means for her future if she stays with him and he does this again or she later finds out he was lying or she just never feels safe and comfortable with him again.
It's a bit like the advice on supporting someone in an abusive situation, you give them the opportunity to share the scary thoughts and feelings with you, knowing they won't be judged or told what to do. Rather than avoiding it completely or glossing over it when they bring it up so they end up feeling they can't talk about it with you.
Don't suppose she knows how long the call to supposedly tell the supposedly crazy woman to back off lasted?