Barbara Boxer. Is she ok?

I really dont get it with Barbara Boxer. She has been one of my most favorite senators. But I started having doubts about how intelligent she is. Why? She apparently supports the re-election of Joe Lieberman, and in Lieberman's campaign site she is listed as a "Joe supporter" with this quote:

"I have seen first hand Joe Lieberman's tireless work to protect our air, water, land and other precious resources."

Anyway, I still like her despite that, because I dont think she does it for personal gains. She is clearly one of the most liberal senators and a person of very high integrity. I simply start questionning if she is out of touch with reality. Lieberman is terrible for the democratic party and should (and will) lose the election. The positions of Boxer are in reality very anti-Lieberman, but she seems to be naive enough to support him because he comes across as a nice guy? What's her problem?