I was wondering that myself. Maybe she wanted to do a Naruto character and didn't waht to dye her blonde hair or wear a wig?

It's certainly not a bad costume by any means - she did a great job with it. It's just that with a whole wide variety of possibilities open to her as a tall, thin woman, she chooses Tsunade? I can't tell her age at all from the pic - maybe she wanted to cosplay someone closer to her age than the average anime character, or perhaps Tsunade is very close to her personality and she wanted to cosplay her because of that. I think I'd at least have stuffed my bra, though. :)