Questions about recommendations

[PNM1995]

Hi everyone- I was wondering if anyone might know how letters of recommendation work? I have a friend who's going through recruitment at her school and wants to get rec letters for Phi Sigma Sigma, but neither of us know any alumna. Is it frowned upon to ask for one on here? And if it is, can anyone tell us the proper way to go about finding someone to write a rec letter? She got one for another sorority that had an online form; does Phi Sigma Sigma have something like that?

Thanks so much!