Relocation: Mother Wants to Move to Florida with Our Six Year Old Son

My question involves a child custody case from the State of: Texas

I have a current visitation order (my son's mother is the custodial parent and we share all other responsibilities) that states that neither of us can move outside of our current county of residence without the others consent. She is now wanting to move to Florida to live with her new fiancé and wants to take our six-year old son. My son and I are very close and moving half a country away would devastate both of us.

My question is this: can she ask the judge to modify the court order to allow her to move away? She has NO family or friends there (aside from her fiancé, that is nine years older than her older son). How easy would it be for her to accomplish this and what recourse will I have to prevent it?

I am not trying to interfere with her life, I simply cannot live that far from my son.

Thank you in advance for your advice.