How to be there for someone

I have a friend who is going through a lot right now. She will post on her Facebook sad things, and I always want to reach out to her or comment on her stuff to let her know I'm here for her. But I honestly never know what to say, I'm great at listening and I truly do care about her well being, but I just suck at actually reaching out to people and showing compassion I guess? I just never know the right things to say. So it's like should I even say anything? Do I just let it go? I don't want her to think I don't care, or I'm just silently watching her on Facebook I guess, idk. When we get together it's always play dates with our kiddos so we don't ever really talk intimately. I just want her to know she's not alone, that I'm here for her to at least just have a listening ear.