What can I do if my ex-wife doesn't let me see my daughter and we have joint custody?

If you have joint custody, you should have a court-ordered schedule on when your daughter stays with you and when she stays with your ex.  Further, joint custody should also involve child support.  If your ex will not allow you to see your child, you need to consider going back to court and filing an order for either modification to seek sole custody or indicating she is in contempt of the original order.  Either way, you will need to appear before the divorce court judge to attempt a reasonable solution or find your ex in contempt.

If your ex wife does not let you see your daughter then you may make a motion to enforce your rights to see your kids.  the court will do what is in the best interests of your daughter, not what your ex wants.  the court will take into account that there is a need to keep your daughter in joint custody so that both you and your ex have the right and access to be in your daughter's life.  your daughter needs to have a mom and dad growing up and the court recognizes this and does not want one parent to try to penalize the other by taking away their child.  I suggest that you hire a lawyer. most family lawyers will meet with you for free the first time.