I was intentionally not playing aggressively, both because of the rating gap and because of my unfamiliarity with QGD-type positions. This is an area on which I expect to work further in my opening study and training games, due to the likelihood of running into QGD setups in the future. However, I was satisfied with my opening play until around move 12 and was objectively fine until move 16 (somewhat ironically it's a d4 pawn move that gets me in some trouble, despite my avoidance of a Queen Pawn game structure). At this point, my lack of a coherent plan shows and Black takes over the initiative. However, both of us then focused far too much on Black preparing the pawn push ...e3, which at the time seemed to be the major threat, passing over other intermediate moves and possibilities.
As often occurs in competitive games, one player (in this case me) is prone to blunder when the psychological pressure is released after working through a difficult sequence. Once I survived ...e3 my sense of danger vanished, with unfortunate consequences. A useful lesson that will remind me to re-set my thinking and check for new threats after such sequences.
My opponent was quite gracious in victory, as she also thought the game was interesting, especially the tactical ideas surrounding the ...e3 push, where even if I missed some of the possible ideas for Black (e.g. b5 which would have prevented my use of the c4 square) I was able to see most of the variations, set a trap of my own, and emerge with a difficult but not lost position.