Friend definitely did nothing wrong. I'm glad she told Cousin what she saw.
I second the suggestion of discreetly calling another friend or relative of Cousin and asking them to check on her, not mentioning why but just that "she seemed down lately" or something--if her money troubles are well-known in her circle they might assume it's entirely related to that. I think Friend should leave Cousin alone for a few days (no messages), but having a more neutral party check on her would alleviate Friend's reasonable concern about Cousin's safety and emotional turmoil.
Mikayla, interesting perspective. I do think you have a point, but for right now, I would advise Friend to try and remain on Cousin's "side," and not angry at her, especially as this all happened so recently. If Cousin calms down, gets some perspective, realizes Friend was trying to help her and all that, she should definitely apologize to Friend for what she said. I would hope that happens soon; if not, it may mean Cousin has decided to sever their relationship anyway.
I wonder what prompted Husband to come home early? Was it just coincidence, or did he somehow know Friend was going to be there? Also, it seems like he did not offer his wife a preemptive explanation of the restaurant events, or surely she would have mentioned it...