Look you aren't going to like this, but at the time she was saying/doing those things, odds are VERY damn high that the emotional affair and probably some degree of inappropriate PA (phone sex, etc) had already started and she was making her comments based on things that XH had shared with her. They probably commiserated about their pain and misery, only they could understand the other's pain, etc, blah blah blah. Acting giddy, like a teenager, etc... are signs of at least an EA in full swing, not of an envious neighbor.
You really don't want to let go of her being the problem in your M rather than the R between you and XH, huh?
