I'm sure that pumping on a flight was not that woman's first choice, but it might have been her only choice.
Travelling without her child, early in the morning, her breasts would have been full and uncomfortable. Someone who's experienced that would understand just how uncomfortable it can be. (Been there, experienced that.)

If the flight took place at a time when she would normally have been feeding her child, her breasts could have "let down" and leaked milk onto her clothes - embarrassing and uncomfortable. It's not like controlling your bladder - a woman can't prevent this from happening. (Been there, had it happen.)

While I sympathise with the OP's desire to sleep on that flight, I sympathise even more with the woman.