What should I do if my ex sent our daughter to another state to stay with her grandparents without my knowledge or consent?

You should file an action (or motion in the cause to modify custody if a court file dealing with custody already exists). If the grandparents seek to intervene you have a superior right to them with respect to custody of your child. Natural parents have a paramount right to the care, custody and control of their children unless they have engaged in conduct inconsistent with this paramount right. This is fact dependent.

As between you and your ex-spouse, the court will use a best interest of the child test. I don't know all the facts, but the court is certainly going to be interested in why your ex-spouse voluntarily relinquished her parental responsibilities.

It is hard to answer this question with out knowing more  So I am going to state some general rules: one parent cn not interfere with the custodial or visitation rights of the other parent.  Also, a parent can not take a child out of state with the intent not to return.  Now, your agreement will also have a place in this answer so consult with it and with your attorney. Once you determine why she is there and if it is interference with you rights you will know how to proceed.  Good luck.