yes, it is a fact she forgot, but it is also a fact that you don't feel very well right now.
I know when I am depressed, or in a low mood as you say, things hurt much much worse than they otherwise would AND I adopt resignation as standard operating procedure. It's strange. Depression is weird.
It's hard to get a hold on some perspective. Yeah, I know I can "think" correctly, but sadness and melancholy color everything. The feelings can be overblown.
I know when I'm feeling well, my therapist forgetting something would elicit a response from me of "you nimrod, were you paying attention at all? Geez, I want my money back for those sessions!

"
When I'm not feeling well, forgetting would be a harbinger of doom - because everything is a harbinger of doom when I'm depressed.