Upvote:3
Given the diverse nature of airline staff, I highly doubt there was any 'profiling' going on.
If your GF is a less than frequent traveler, it may have been the case that she's is boarding near the end of the queue, when overhead space is becoming scarce. Was she also encumbered with other items beyond what would fit under the seat such as a coat, large handbag, etc?
Gate Agents tend to be much more hawkish in the winter.