Part of the answer as to why she doesn't use the designated space may lie in the nature of the "designated space". On campus, most of the lactation stations are in bathrooms.
If she has reasonable privacy in her cubicle and nothing is showing, I don't see the harm. More convenient electrical outlets, more comfortable chair, counter space, and she doesn't have to listen to toilets flushing while she's pumping. Plus, she's not taking time away from work (which is what people are usually ******** about).
Just ignore it. Livestream music to headphones if the noise of the machine bothers you. And applaud her for her dedication to motherhood AND job.
yeah we have a total of two and both are adjacent to the bathrooms. It's just a partial swinging door separating the very small nook so anyone using the bathrooms likely gets a glimpse as they go in and out. I'm assuming the ones at OP's are nicer just due to the volume they have, but if it's like ours.......yeah, I could see just staying at your desk. Especially if you are someone who takes longer to express and you'd like to get some **** done so you don't have to stay later.