You can send a gift or a greeting card to her. Try one of these adress:

Liv Tyler
c/o Mark Urman
DDA
1776 Broadway Suite 1600
New York, NY 10019
USA

Liv Tyler
C/O Creative Artists Agency
9830 Wilshire Blvd
Beverly Hills, CA 90212
USA

We know that she gets a lot of fanmail everyday, so maybe she doesn't have enough free time to read all of them, but it's worth a try.