I understand that him calling himself "Ben" to her means that she didn't realize he was Obi Wan, but I also think it was stupid that she wouldn't recognize him when she's asking for his help between 8-10 years later (even if he did age 30 years in that time).
I don't understand this objection. She makes a recording to send with R2 to ask a guy she doesn't know for help. She doesn't see him except for a couple of seconds before he's killed by Vader on the Death Star. Why would she recognize Obi-Wan Kenobi as this Jedi 'Ben' who saved her when she was a kid. Except for the fact that obviously Bail would say something like "Go to Tatooine and retrieve the Jedi who rescued you when you were kidnapped as a child" not "Go to Tatooine and retrieve Obi-Wan Kenobi, a Jedi Knight you've never met" at the end of Rogue One.
This is what I mean - she would have known who he was now that they’ve introduced this. So her not knowing it’s the same guy is silly. Likewise Obi Wan’s reaction - where he doesn’t seem to have any idea who she is personally even though he met her less than a decade ago.
