That would be interesting if that were the case between Don and Megan. I guess I'm still trying to reconcile if the plan was for shopping to be done that day (I have to rewatch to get a refresher on which day the shopping excursion took place) and the money-asking occurred on another day. Emile's visit to his publisher (the day Megan also asked Don for money?) was on Friday? And the women's shopping trip for gowns was Saturday? Or did the money asking also happen on the shopping trip day? I'm wondering because if they both occurred on the same day, wouldn't that mean that Megan had cash at her disposal anyway?
As someone else said, she might just have found herself needing cash she didn't have. But I wouldn't be surprised if it was a set up where Megan considerd the money she made "her money" while Don's salary was "their money." And Megan's money was reserved only for things she did for herself/entertainment or whatever. Like throwing Don's surprise party (so he doesn't know about it) or buying her wardrobe. That seems very common, especially on TV.
I wonder if they would have though. I mean, their frustrations with Megan being Don's wife are real (and I think somewhat justified), but Stan, even in his anger, was able to concede that her pitch for Heinz was better than theirs. I think ever since his weekend with Peggy in the the hotel room, Stan has rethought being dismissive of someone's ideas simply because he doesn't get along with them. And we really haven't seen Stan not getting along with Megan; he's cordial to her, if anything. So, I think it was Megan's own fear that prevented her from even going through the proper channels for pitching ideas because she's insecure in her position as junior copywriter whose husband's name also happens to be on the lobby door.
When Don tells her it's a good idea, she asks him to take the credit because she believes that if the idea is perceived as hers, it will be dismissed. The theme of the season is "every man for himself." The idea that Stan or Ginzo would shoot down a good idea because it came from someone they don't like or respect, even if it's bad for the agency, seems totally consistent with all the infighting we've seen.