Hello Jess,
This is a tough question to answer. Not meaning any disrespect to Catholic brothers and sisters here, but the mindset of some RCs is difficult to get into.
I'm a baptised Catholic. My immediate family left the RCC some years ago. Catholic Charismatic movement- filled with the Spirit, then found it increasingly difficult to fellowship in the church we we in.
Reaction of wider (still RCC) family was hostile. One beloved Aunt who was kind to me as a child went to her grave never again speaking to any of us. Would walk past us on the street. Some spread falsehoods about us. Still hurting about this today. In fact this was probably the worst hurt I've ever had.
Some thawed out many years later, mainly when they stopped going to Mass themselves. Not because of a spiritual experience, but because of their regular hangovers from the Saturday night. Lots of drinkers in the family. It was more acceptable to stop going to Mass because of alcohol abuse than because of Spiritual reasons. Did eventually get invited to a Wedding, few indeed of the family went out for Holy Communion though. Perhaps hence the invitation.
When contact was eventually renewed and some relatives asked us why we left the RCC we shared the gospel with them and two at least were born again. Not to say anything bad about the RCC, we didn't mention the RCC to them at all. We mentioned Jesus. The Free Pardon God speaks of through the Prophet Isaiah was ace for giving them peace at the end.
Again, I hope any Catholic brothers and sisters here don't take offence. I'm sure they're sincere believers and have fine churches and Catholic relatives. I wish them well. This is just my testimony.
Based on my testimony I would advise caution. Your mother hasn't been attending Mass or confession for many years, but she still might consider herself Catholic in a sectarian sort of sense. This can be a powerful and irrational motivation.
My cousin George reportedly told my Uncle many years ago he considered confession nonsensical, his exact words 'making up some expletive to tell the priest'. George remained in the Catholic church and did not talk to us for TWENTY FIVE YEARS even though he used an expletive to refer to confession. His Spiritual condition I would say (and he would probably admit) is Nil. Yet there was this irrational sort of hostility. Them and us.
So I would advise caution. Pray for guidance and for your mother. Pray that she may be born anew. Also be blameless in your relative's eyes, give no cause for reproach. Love them, forgive them. Move slowly, do nothing in anger. But stick firmly to your principles.
The Lord works for the good in all circumstances. I met a Lady, a former Muslim who found Christ and was disowned by her family. I could relate to her and encourage her because I too was disowned by family.
Though my father and mother forsake me, the LORD will receive me. (Psalm 27:10)
God Bless