Athena and marriage

Last weekend we were having dinner at my mom's house with my bro/SIL and family and Athena and her cousin O were talking about getting married. O has a plan of marrying Athena. Athena started to respond to this (and I thought she was going to say no, they couldn't marry, but this is what she said instead):

"Two girls can only get married if one of the girls looks like a boy." She went on to say that O did in fact look like a boy so that they could get married, and both seemed happy with that plan. I keep wondering if she made that up because of an observation, or if she just made it up because it made sense to her. Either way, it made me laugh.