In most states, and I would hope in your state, if you feel that your GAL has an unfair bias toward one side or the other, you can petition the court to dismiss them, and ask that a new guardian be appointed.

You should not have to tolerate being lied about by a representative of the court! That is unethical, unprofessional, and I do believe illegal. If she's chosen "his" side, well, he's in for a rude awakening when she's replaced. I recommend you take this to the court ASAP, and good luck to you!