I think asking forgiveness from the dead is a Catholic and/or secular humanist belief. I don't share it.
My main proposition is children need to be brought up in the admonition of the Lord (Eph 6:4), and not be confused by household gods (Zech 10:2). Scripture supports that view, but some ppl can't handle it because it requires repentance.
Failure to do so is a complete failure as a parent. (Deut 6:7, 11:9, Psa 78:5; Josh 24:15)
No I think you have to forgive even though she is dead....only in the sense that you have to gain an understanding as to how she got to be the person that she was. By understanding that you can become a “dam” in the progressive flow of time and staunch the effects of generation sin(like my brothers and I have all purposed in ourselves to do).
Also she is not dead...and you know that from scripture as well. She went to hell if she never accepted Jesus as savior and repented but her spirit animus is still alive. So you can still forgiver her, and what ever you remit God will remit. You can still pray...”Father forgiver her for she didn’t know what she was doing to me”.. We don’t really know how far our prayers will go in saving folks and God is able to go backward and forward in time in ways we can’t even imagine. So forgive her...77 time 7 if you have to. You’ll feel better for it....I know! I’ve done it myself!
I’m not Catholic by the way...I’m Bible all the way....but God while he acts providentially also acts tactically and dynamically across time dimension heaven and hell. We only can view time as being one day at a time going from back to present and then into the future. Some Christians became Christians literally at the brink of death when they saw Hell opening wide for them and they cried out to God and he saved them and they came back to tell the rest of us about it. How many more have done so, got saved “by the skin of their teeth” as the Bible says, but didn’t come back? Who knows....only God!