If you pass before your daughter becomes an adult, most likely your daughter's father would have custody of her until she reaches the age of 18.In your Will or trust agreement you can make a request that your mother be the guardian of your daughter should you pass before she reaches 18. However, if the father survives you in such a situation then most likely he will end up having custody. To circumvent such, you and your "ex" could have an agreement drawn up by a family law lawyer stating that if you pass when the child is a minor, then your mother becomes the guardian of the child.Such can be drawn up and resolved outside of the court room. The court cannot force the agreement that you suggest with respect to your mother being the guardian.