My daughter Emma and I were climbing the bleachers in a middle-school gym, getting ready to watch her brother Elliot play basketball, when we spotted my husband’s ex-wife.

“Mama Jean,” as we called her, was sitting a few rows up with Elliot’s twin sister, Chloe.

The twins are my husband’s from a previous marriage. At three-and-a-half years old, they were adorable ring bearers in our wedding. We had Emma a year later. The twins lived with us half the time, and our daughter idolized them.

So when she saw Chloe and her mom in the stands, Emma started tugging my arm and doing little jumps.

Approaching their row, Emma waved and said brightly, “Hi Mama Jean! How are you?!” ‘Just like we taught her. So grown up!’ I thought to myself.

My husband’s ex-wife glanced at my daughter, a five-year-old in polka-dot leggings, and looked away without saying a word—as if we were invisible.

Emma stopped waving and looked up at me, confused. I was stunned. The moment stretched. People nearby went quiet.

Before she could try again, I put my hand on Emma’s shoulders and steered her up the stairs. “C’mon sweetie, let’s keep going to the top,” I said, my cheeks burning.

“Mommy, why didn’t Mama Jean say hi?” Emma asked.

None of the books I read on “blended families” mentioned how to handle your husband’s ex-wife insulting your child—in front of a sibling, no less.

Obviously, you don’t create a scene in a middle-school gym. Everybody knows that. But telling your spouse about it later will only create a scene at home — after all, what more can he do? He already divorced her once.

So you bottle up the emotion and hope to find a sympathetic ear later in the week…or month.

“That wasn’t very nice, was it, Mommy. If someone says hi, you’re supposed to say hi back,” Emma recited to herself.

I knew being a stepmom would be difficult at times, but no one prepared me for the rage. It comes rushing over you, fast and hot. You may experience it as prickly pain or total numbness, a silent scream, shortness of breath, or a momentary lapse in the time/space continuum. Don’t worry, you’re not having a stroke — not a medical one, anyway.

“Right, Mommy?” At our seats, my daughter was still chatting about manners.

“Maybe she didn’t see us,” I choked out, stabbing a juicebox with a straw. “She was probably watching the basketball.” Nevermind that the game (stab) hadn’t even (stab, stab) started yet. (Stab!) Sigh.If only they made juiceboxes for grownups — filled with margaritas.

I had made friends with a few other stepmoms, and I knew this was another one of those incidents only they would truly understand.

The four of us started getting together about once a month, usually for coffee or drinks, or the occasional mani/pedi, to talk through these humbling/frustrating/mind-blowing situations none of our other friends could relate to. Gradually we met other stepmoms at the playground, at swimming, at soccer. And we realized that, like it or not, we were in a club of our own: the stepmom’s club.

Collectively, we had combed through volume after volume of clinical wisdom by therapists and PhDs, searching in vain for honest portrayals and realistic advice for life in a blended family.

Instead of finding answers, we found there were lots of common trials that most stepmothering books left out.

Like, what to do if the ex is routinely late (or early) for joint-custody pickups and drop-offs? Not three hours late, not missing in action, just consistently 60-to-90 minutes on the wrong side of the court-approved time, disrupting family dinners, movie nights or family getaways.

Hint: Even if you are in the right, it’s usually not worth calling the lawyer for this one. Trust us. Just adjust everyone’s expectations. Accept that the siblings’ reentry into your home will be bumpy and make dinner plans that can go on with or without their timely arrival.

Sometimes you can follow a book’s advice and still end up in tears.

In our family, we had the “names and titles” discussion early. The twins decided to call me by my first name. We’d call their mother Mama Jean. Emma referred to the twins as her brother and sister, and I just called all three children “our kids.” Easy-peasy, right?

Until one day at an ice cream shop, the elderly lady behind the cash register looked at the three sandy-haired children in front of her and said to Elliott, “And what are your sisters’ names, young man?”

Looking at his twin, Elliott said, “Well this is my sister Chloe.” Putting a hand on Emma’s shoulder, he said, “And this is Emma. But she’s only my half-sister.”

That one stung. I couldn’t see Emma’s face, but my eyes welled up. And we were having such a good day!

The sweet lady looked quizzically from one kid to the next and said, “Hmm, so which half is your sister, the top half or the bottom? Right half or left?”

Elliot looked confused, and she said, “I have an adopted sister, but we never call each other adopted sisters. Just sisters. You don’t need to say half, do you? She’s still a sister, so why not just say sister?”

Power to Elliott as he nodded and said, “Makes sense.”

Sometimes the hardest thing you can do as a stepmom is to say nothing. The kids were absorbed in their ice cream cones — clearly they’d moved on from the conversation — but I still had a lump in my throat.

Over their heads, I silently mouthed the words “thank you” to the nice ice cream lady.

Months later, I learned from Chloe that their mother went ballistic whenever she heard either of them call Emma their sister. In her house, they had to refer to Emma as their half-sister or just plain Emma. Well that explains it, I thought.

How can you get mad at a kid put in that situation? And what do you say? Once again, I was stunned into silence, feeling totally unprepared for the emotional minefield of stepmotherdom. This “situation” was definitely getting shared at the next stepmom’s club meeting.

Over time we learned that all of us stepmoms had independently started our own list along the lines of, “Things I wish I knew before stepping into stepmotherhood.” We began compiling the lists with the idea of someday creating a book for stepmoms by stepmoms.

Ultimately I decided not to make an issue of the sister/half-sister thing. I let it go. That’s another thing you learn to do as a stepmom.

But not long after that day in the ice-cream shop, I started hearing Elliott refer to Emma as his “little sister” — which filled me with this giddy, irrational joy. Even when he’d call her, “my annoying little sister,” part of me was secretly pleased, and I wouldn’t correct him. Is that wrong? Maybe I’ll ask about it at our next meeting. Or, maybe I’ll just let it go.

Kendall Rose is a finance professional, a mom and a stepmom based in St. Louis. Her first book, “The Stepmom’s Club: How to be a Stepmom Without Losing your Mind, your Money and your Marriage" was released May 1, by Sourcebooks.

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