Living in the past

Tamarra
My mother lives in the past. My family has a lot of arguing and issues that she holds onto and constantly brings up every time we hangout. And if we(her children) don't agree with her side she says we aren't loyal to her....we've told her before that she needs to let it go. She has so much pent up frustration from what happened in the past. She says she's done with it and she's not going to talk about it or let it bother her but in the end she just does it all over again...
Any ideas on how I can talk to her about our concern?