Well I was born on the 26th November 1951 and my father, born on February 1st 1920, insisted from my first birthday that my birthday and Christmas presents were not to be combined.
He had watched his elder sister and younger brother receive separate birthday presents ( the one in August, the other in March) while he was given combined presents.
So no, the young mother is not being rude or "entitled" simply expressing a preference which is sensible. Her manner may have been unfortunate - that I cannot judge, but the principle is good enough, and as the two dates given above clearly show no new thing.