I have to relocate for 4 months for my job, and me and my ex share joint physical/legal custody. She is?

refusing to allow my daughter to come see me on 3 week on 3 week off basis. Currently we exchange every week. I have asked her to modify to every 3 weeks because of airfare costs and she won't budge, no compromise. I told her I would pay all travel costs and I have been 100% faithful with my child support payments. Her basis is that it is "unhealthy emotionally" for a 3 year old to not see her mom for 3 weeks completely ignoring the fact that she won't see her dad for 3 weeks at a time either. I've tried so hard to work with her but she refuses to talk in person and when we do talk on the phone it results in her hanging up because she can't confront "tough" issues and talk them out. What do I do? Can she refuse that when it's because of my job I'm relocating and that it's a temporary move and I'm willing to pay for all transportation costs?