I'm confused about primary and secondary health insurance?

My daughter is on my policy, where all of the payments come out of a fund set at the beginning of the year, so if it is $1,000 that can be wiped out by one trip to the ER. Also, she is on her father's plan which is a taditional co-pay plan. Would it work out to my advantage to use his at primary and mine as secondary? Can the co-pay requirement from his insurance be paid from my plan?
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Here are the rules of the National Association of Health Insurance Commissioners. These rules are listed in order - the first one to apply to you will be used to process claims. 1. If the Policy Holder is the same for both contracts: a. The plan that covers the policyholder as an active employee is primary. b. If the policyholder has the same employment status (active/retired) under both plans, the plan with the earliest effective date is primary. 2. If the Policy Holder is the spouse or domestic partner: a. The plan that covers the policyholder as an employee is primary. The spouse's is secondary. 3. If children are covered under more than one policy and the parents are married or living together: a. The policy of the parent whose birthday (month and day) is earlier in the year is primary. b. If the parents share the same birthday (month and day), the policy with the earlier effective date is primary. 4. If children are covered under more than one policy and the parents are divorced or living apart: a. The policy of the parent that the court has made responsible for health care insurance is primary. b. The policy of the parent who has custody of the children is primary. c. If the court has not placed responsibility on one parent to insure the children and the parents have joint custody, the policy of the parent whose birthday (month and day) is earlier in the year is primary. If the parents share the same birthday (month and day), the policy with the earlier effective date is primary. d. If the natural parent elects to have coverage under the policy of the step parent, we will consider the policy to be that of the natural parent. These rules do not apply when one policy is Medicare. Your state laws may vary.
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