I have an alternate suggestion instead of the identical spamming: how about everyone just sends a tweet to her telling a little about themselves, fav album, song, where you're from, etc. It's not hard, and it would be more interesting for Ayu than just getting "omg! have a concert near me!"
For example, I just posted this to her:
nambuchou @ayu_19980408 Hi Ayu! I've been a fan of yours for over 4 years, from North Carolina! <3 Rock'n'Roll Circus; Don't Look Back is my favorite.
(Dear lord, I joined twitter. The power of Ayu!
)
If you tell her where you are from, it's a way to subtly point out you are an international fan.
