Are you guys aware that Ashley Eckstein did a cosplay as Ahsoka for a photo shoot last year?
Ashley as Ahsoka
My suggestion that they cast her took that into consideration.
She has the same level of resemblance to the cartoon character as Ewan McGregor does to Sir Alec Guinness, meaning close enough.
Plus, there's always the magic of CGI that could play a factor. Naturally, Ashley sounds exactly like Ahsoka for some "puzzling" reason.
Of course, all this would be pending auditions, etc., not to mention we don't even know whether there are any live action Ahsoka adventures in the pipeline.
Another possibility, that I'm sure they'd consider, is they might split the difference, and use a different actor for the physical stuff, but still call Ashely back to do the voice. They might even try to Jar Jar her, that is more than just simply tweak the physical actor's basic appearance.