Woman messaging my husband

What do you all think? My husband and I keep our phones, social media etc open to eachother. I've noticed a woman messaging him time to time on Facebook while using the iPad. She is also married with a baby under a year old like us. The messages are always asking how he is and how things are. I notice he will respond with very generic answers but she continues to want conversation and ends up writing what seems like novels on how she is. She has also in the past asked if he wanted to come boating and when he responded that his girlfriend (me at the time) had to work, she responded that "she doesn't need to come". This just doesn't sit well with me. I even recall when we first starting dating that she posted on his Facebook wall "I had a dream about you lastnight! How weird is that?!" Why does she need to message MY husband every so often to catch up? We don't get together with her or her husband and I've only met her twice. Am I overreacting? Could she just leave my husband alone and message her own? He has since deleted her from his Facebook when I said this is really bothering me.