We don’t know her upbringing or struggles, which may inform her behaviour as an adult.
Growing up in poverty in a large family, we learned to view food/ treats as a scarcity. I and my siblings would eat very quickly to increase our chance of getting any leftovers before they were gone, so we didn’t go to bed hungry. Added to that, my parents were immigrants so didn’t always know or correct us on British cultural etiquette.
My attitudes to hoarding and scoffing any food in front of me because it might not be there the next day, lasted well beyond my childhood periods of poverty and well into young adulthood.
Whenever I was in social settings outside of the family, I had a habit of eating as much as I could in as little time possible, even if the food was meant to be shared. In my mind this was fair game because I assumed everyone else did the same as me, so if they waited around to eat it meant they didn’t actually want the food.
I am really grateful for a good friend who quietly pulled me to the side after notice my selfish behaviour a few times, and pointed out to me that I would often eat more than my share, but explained that the correct etiquette was to make sure there was enough to go round for everyone before going for more/ seconds. This was a genuine revaluation to me at the time, and once I knew, I made an effort to do better
That’s all to say, OP’s colleague may well be a greedy CF, but the likelihood is that she is just not aware that she’s doing anything wrong, and her approach to food may be borne out of hardships in earlier life.
A gentle word with her next time OP bake cakes for the office might be all it takes to solve the issue.