You are correct. The "sense of the faithful" is active in your Catholic relative! Certainly, we must both agree that our love will be even greater in heaven - and nothing can separate us from the love of Christ. Thus, her father remains part of the Body and even more deeply desires her daughter's salvation and God's graces to rain upon her. I believe this is a comforting doctrine for those who have lost a loved one. A connection still remains between the two as a result of their love. (which is from Christ)
Please forgive my ignorance, but I don't know anything of the exact Church teaching of purgatory. Who goes there? Why? What's it like, and for how long? What is the strongest scriptural support for this, or is this considered tradition?
What Purgatory is I can tell you from the top of my head, but more Scriptural/Tradition quotes will have to await written sources that I don't have with me. Even several hundred years before Christ, Jews believed (at least Pharisees) that the souls of faithful men who had deviated somewhat from God's ways were subject to a third state of existence. Maccabees 12 talks about some men who died in battle with some amulets with them. Judas, the leader, took up a collection of money and sent it to the Temple and the men prayed for the souls of these men who died with the taint of idolatry on their hearts. The Scripture itself explains that there would be no point in praying for these men if they were in hell or heaven. Jesus also implies the existence of a third state between heaven and hell, as does Paul. Being that the first Christians were Jews of the Pharisaical branch, it would follow that they had similar beliefs as laid out in Maccabees. Practices noted in later writings show the validity of the teaching.
The idea is that nothing impure shall enter heaven. We must attain holiness - how can we come into union with God and not be holy ourselves? Before I continue, be advised that this is not holiness we attained ourselves, but through God's graces throughout our lives. When we are judged, God will note whether we have purified ourselves in this life. Is it possible we can attain union with God but have pride? Have sloth or vanity? Hardly! We must become like Christ to rise with Christ. Purgatory is a great mercy, because it gives us, the saved, a final opportunity to prepare ourselves for eternal life. We do NOT merit in Purgatory. It is a purging - which entails suffering (just like any purging or sacrifice does). But we know that we are destined for heaven. We will deeply desire to be purged of anything that keeps us from Christ. It is the result of Christ's work of redemption on the cross.
The Church doesn't officially teach much about Purgatory's means of punishment, or "length of time" spent there, and so forth. Private revelations given to others give us an indication that it would be better to be purged here on earth! But these are not part of the Deposit of Faith. The Scriptures and Apostolic Tradition don't teach us such things. So all we can do is speculate on the particulars.
Let me know if you want more specific Scripture/Tradition quotes.
Regards
Thank you for the "purgatory primer". One thing I'm curious about is to what extent people go there. (I think our side would say that the blood of Christ covers our unholiness and that the saved are seen as righteous in God's eyes, thus no need for purgatory.) Since we all sin after salvation (or initial salvation) then does every ultimately saved person go to purgatory for a time? Or, does everyone who was "right" with God and had confessed all sins before death get to bypass purgatory? I'm just trying to figure out if purgatory is expected to be experienced by very many or very few.