My office manager is sabotaging me and no one believes me

I'm convinced our office manager is intentionally messing with my schedule. She double-books me, "forgets" to confirm appointments, and when I bring it up to the owner, she plays innocent. The owner trusts her completely (she's been there 15 years) and thinks I'm just being difficult. But my production is down 20% because of scheduling issues and I'm the one who looks bad. I don't know what to do. I can't prove it's intentional but I know it is.