Should I tell her about her poor use of grammar?

An acquaintance from high school is one of my facebook friends, I haven't seen her much in the past 15+ years but we do chat in FB. Her posts (that everyone sees) are filled with grammatical errors, she uses " 's " for every plural word as in "The dog's are barking" - it drives me crazy!!! I am not expecting perfect grammar and I know it is an informal setting but I think this is basic knowledge. Should I tell her that she is wrong or just try to ignore it? I would do it in a private chat or email, not as a post on her wall.