I think therapy is the way to go.
Humans rarely successfully verbalize what they really mean. Children can be expected to have even less skill in this area. In addition, kids grow up having certain belief systems based on their interpretation of events and relationships during their youth. There is too much room for miscommunication, wrong interpretation, exaggerated beliefs and hurt feelings without open communication. If you aren't a trained psychotherapist, there's a good chance your efforts could backfire. And I agree with the posters below, that the talk with your 8-yr-old about it being wrong that she doesn't show you the right amount of affection, probably wasn't age appropriate.
I watched a similar scenario play out. DH's ex filled their 3 daughter's minds with negatives about their father. Therapy was never considered (except one time when we had 1 of them live with us, and it was my idea to foster open communication, and it helped). All 3 have been extremely loyal to their mother, despite allegations of abuse (they lived in another country with her, so nobody really knows what happened).
Along the way, all three exhibited behavior which most adults would not tolerate. However, because they were stepchildren and because my husband felt the typical guilt feelings, their behaviors were not addressed. Likewise, since my DH didn't address their behaviors, I couldn't really either because I'd just be the classic evil stepwitch. So I wound up sick to my stomach each time they'd come to visit, take over our home and deliberately be nasty to me and our son.
For many years, I looked forward to the day when they would become adults and stop the hate campaign. Their ages are now 27, 25 & 22. Unfortunately, since noone addressed their behavior, they grew to believe it was acceptable. A few years ago, I pulled back. I rarely see them. In my mind, their lack of maturity is no excuse for continued abuse towards me. My DH can see them when he wants, and they can visit us anytime they want (although they never do, since it's much more difficult to get away with obvious obnoxious behavior under our roof). The oldest and the youngest sort of get it now. They can at least be civil to my face and I don't care what else they think or say.
The middle one, however, is the lone holdout. She is still a small child trapped in an adult's body. She's the consummate victim, she blames others for everything that happens to her and she has a horrible track record of maintaining any sort of relationships. She's known as the "sensitive" one, yet can muster up more venom in an instant than a pitbull. She constantly stirs the pot by having her sisters or her grandmother pass on nasty messages or accusations about me. Her world revolves around her. That's natural for small children, but is considered arrested development when it continues at her age.
My point is, as her parent, one of your responsibilities is to teach her how to have successful relationships. I tried raising that red flag long ago. Unfortunately, my DH was more concerned with only having positive experiences with them than teaching them. I told him I predicted they'd all have troubles in relationships if they grew up thinking they were justified in treating others with complete disdain and disrespect. Again, guilt won. Now, my DH is not too pleased with their behavior. They constantly do things that remind him of the opportunities he passed on to teach them. Although 2 of his daughters have learned to act civil to my face, all three are stuck in "survival mode". When someone can't think of others, it makes having any sort of relationship difficult and usually short-lived.
Disney Dads do their children no favors. Stepfamilies are far too complicated for the majority of individuals to deal with successfully. Therapy should be mandated for all.
And for stepmothers, how easy it is for us to be demonized!! Wow, I was a she-devil the minute I got married, literally. We had our wedding out of state. DH didn't want to complicate HIS normal summer visit with the kids, whom he flew to the states for 6 weeks in the summer (along with their mother), with our wedding. They went back home in August. We got married in October. Found out later, they all despised ME for not inviting them to be IN MY wedding. This was apparently a HUGE factor in the uprising of their hate campaign for me. It was DH's decision, as part of his mission to shield his young children from the acceptance that he was getting remarried (all 3 children hung on to the hope that he'd get back with their mother for many years after their 2nd divorce). Of course, their mother comforted her babies from that mean and nasty witch who just stole their daddy. See? A little open communication with a professional could have quieted some of that building hate.
Never really good for children to learn (or be taught) to hate. Better to have dialogue, under professional guidance.
Wow, so long. Sorry!