What have you guys found to be a good way to minimize the possibility of getting ripped off?
I have a newer OTC that is fairly reliable so far. If I gave her reliability a score it would be 8/10. And last week the SS started - need help with rent... you all know the rest.
I only see her every other month-ish, so if I float her something now, what is a good way to make sure she delivers when I see her again in a month? I know there are zero guarantees when it comes to this type of stuff, but I'd like some opinions nonetheless.


Just thinking this way is acting like a sucker who deserves to be ripped off. There is no "good way" to make sure she delivers when you see her again. There is abundant evidence, through a zillion stories, that you'll get ripped off.
If you want to stop acting like a sucker, here are your options:
Don't give her the money. You owe her nothing, and at least an 80% chance there is no rent emergency and you're funding her drug-fueled vacation to cabo with her boyfriend. Every other month-ish sets up no obligation on your part anyway. Offer to see her again ASAP if she wants to earn it.
Gift her the money. She's been awesome to you, and you don't mind giving this to her as a bonus, even though you know that once you give her this money, you will "pass" her sucker test and she'll keep coming back for more. Still, if you gift it to her, at least this doesn't set up retarded expectations about her paying it back; expectations that are bound to be unmet.
Those are the smart options, IMO. You're just looking to end up angry and disappointed of you give a every-other-month girl an "advance"