Q: My ex and I have a daughter, 14, and we have co-parented well for years. He remarried and now has three more children. Our daughter stays with him during the week for school and with me each weekend, longer in the summer.

He's very laid-back and his wife really runs the show. I often touch base with her because co-parenting with him is like talking to a black hole. At a recent get-together I tried to explain the follow-up to a doctor's appointment and his wife cut me off, saying she didn't really agree with the doctor's approach and wasn't sure she wanted to give my daughter the antibiotics prescribed. I felt discounted and angry. I'm the mother, and I feel something should be said. I mentioned it to my ex, and of course, nothing came of it. Should I say something directly to her? What's good ex-etiquette?

A: For this parenting triad to work, you have to have very specific boundaries. And, since you and your ex's wife perform many of the same duties because of the parenting plan you've chosen, the boundaries have to be particularly clear, or else you are sure to step on each other's toes. This is the reason for Ex-etiquette for Parents Rule 4 (Parents make the rules; bonus parents uphold them). The parents must clearly run the show and the bonus parent (your ex's wife) must clearly support the rules in place.

She must be empowered to make decisions to ensure the children's safety, but within the parameters of the previously established rules.

What I believe might be happening is your ex's wife is the boss in his house and she lost sight of — for want of a better term — the "pecking order." The only way to re-establish that is to have a conversation.

These kinds of conversations are difficult to have. Start first with a frank talk with your child's father, letting him know how you feel, and asking him for suggestions before talking with his wife. I would also suggest he be present. The approach could then be more of "I think we all need to sit down and discuss what we feel our roles should be in regards to raising Bethany." Keep your child's welfare at the center, while expressing your position as her mother. Remember to express your gratitude for her devotion. Don't make it a power play.

Here are some are some tips for talking about co-parenting:

1. Pick a comfortable public place in neutral territory. People are less likely to lose their temper and become threatening when in public.

2. State the problem and have a solution in mind.

3. Listen to their opinion. Disagreement doesn't have to be bad. It can also be the catalyst to coming to agreement.

4. Do not be accusatory. Use "I" messages rather than "you" messages.

5. Keep the child's welfare at the center of the solution. (Ex-etiquette for Parents Rule 1, "Put the children first.")

That's good ex-etiquette.

Jann Blackstone is the founder of bonusfamilies.com.