It's not unusual for victims of incestuous abuse, especially if the perpetrator as a parent, to describe them or even to remember them in idealistic terms. Children are very vulnerable to their parents and they believe that they are the bad one when their parent mistreats them in any form of abuse. Victims blame themselves, and children often view their parents as gods, all-knowing, the epitome of goodness. Because Selena had a "special" relationship with her dad and he met an end that was suspicious, she likely blocked out those memories of him molesting her and cast her mother as the villain. While Dolores was not initially aware that her husband was molesting her daughter, once she did know she did everything she could to get out of the relationship and protect her daughter. However, in many incest cases, the mother is often complicit in one way or another and many victims of father/child incest of either gender are often angrier with their mothers than with their fathers for this reason.
Even when a victim blocks out the abuse, the damaging effects often manifest in other ways, such as drinking/drug use, self-destructive behavior, sabotaging relationships, and sometimes even getting in trouble with the law because they are seeking punishment from society.
Check out another movie starring Jennifer Jason Leigh, the thriller,
Heart Of Midnight
(1988), which was recently released on Blu-ray. Leigh again plays a young woman with a turbulent past, who discovers that her problems stem from suppressed memories.

Selena was OBVIOUSLY in denial, and fighting hard to con herself into thinking her daddy was good.
Such cognitive dissonance (trying/pretending to believe what you KNOW is not true) was driving her to drink, drugs, failed relationships, etc.
So Dolores absolutely did the right thing. She only did it like20 years too late.

Thank you ! You said it in a nutshell. Dolores was taking a gamble, does she let Selena live on in denial or force her to face the truth. My thought was, she would be destroying the good memories her daughter had of Joe by forcing her to remember. It made for powerful watching, I will say.

Yeah, a little jumbled, to say the least, but I see where you're coming from. Without the talk, however, there wouldn't be much of a movie. Selena was in denial, and perhaps, having the truth out in the open, might help her get off her drugs. Or, it might even make it worse, but Dolores was gambling there.
"the greatest Karate Man I have ever known..John Kreese"
Sensei Terry Silver Karate Kid III