It's funny you referenced meth and SILs. I'm about to get married to the love of my life. Her baby sister is an unrepentant meth addict. My Fiance wants her to be a bridesmaid; maybe because the fiance is essentially blind to the problem. (I realized it immediately upon meeting the meth-sister.) I told her NO WAY will the meth head be in my wedding until she gets off the meth, lest she cause a scene and ruin our wedding, or flake entirely and not show up at all.
Suffice to say the entire dialog has caused some friction in our lives.
