Thank you for the insights! I had my GF read your post and she thought it was very good advice.

She is a little worried about causing her father grief by pulling him into a problem that her and her mom are having...but she's thinking on it.

It will be a challenge for my GF to stick to her guns and be assertive and productive with her conversation. She is not a confrontational person, and according to her conversations like this in the past tend to end with them both crying and nothing really changes in the relationship (another reason why my thoughts lean towards a letter). My take on it is that the crying is a distraction from the point of the conversation designed to break the tension and derail the conversation as a whole, so I've been trying to convince my GF that she cannot cry when she has this conversation....all she tells me is that she's not sure she can do that.

Her mom is in a transitional phase right now, they moved out of state (and are away from their three children for the first time) around a year ago. It seems to be that she is quite happy with every part of her new life (the location, the new adventure, getting to explore new career options) except being away from her children and maybe having too much free time on her hands (what a problem! hehe). According to my GF the lack of respect/treating like an adult has been going on for a very long time, way before menopause hit (which it is hitting right now) and the original state of this issues seems to have persisted through. There are some harder things going on in her life as well, and the intention wasn't to drop anything big on her any time soon, but rather to be prepared if an ideal time for a heart to heart conversation presented itself.

I believe she will respect our decisions revolving around christmas, but I'm not sure she'll be happy about it, and I even worry a bit that she will resent me for "keeping her daughter from her". I'm not worried personally about that, but I worry that it could damage my GF's relationship with her mom more, which is the last thing I want.