I don't think you're too short for a day at all- I'm 5'3 and the day looks fine when I carry it. If you do a search on the pics wearing your bbags thread for "day bag", you'll see many pics, including petite people, carrying the bag.
I have the Day (sorry no picture), I'm 5' 9" and was suprised how big it is on me, I guess instead of saying big, I should say long. But I like it. As long as you are comfortable with a long bag, then you'll be ok. I think your height is fine for it, it's just a matter of liking the longer style.
I gotta agree with the others. I am 5'2" and the day is perfect for me. Not too big on my bod, and big enough to hold everything I need. And the most important thing, it is the most comfortable bag I have ever carried.
I'm 5'1-1/2", and avoided the day for ages because I thought it would be too long. I finally gave in and got a Violet day, and EVERYONE compliments me on it, including one friend who has not really liked my BBags before, but now digs it.
i've said it before and i'll say it again!! reason why the day is so amazing is that it slouches and molds to the person's body, hence looking proportionate no matter what. unless u stuff it with a pillow or something of course.