Absolutely. If the bag would not fit in the overhead bin, and she would not let them check it, what did she expect?
United Express normally flies regional jets, not what we consider a “big” plane.
My laptop bag will not fit under the seat on RJs so it has to go into the bins above. Sometimes if I have it overstuffed or not arranged well, it won’t even fit into those bins.
It’s the main reason I now fly mostly Southwest. The bigger Boeing jets make flying easier.