I personally agree with many above that unless the aunt in question is the legal guardian,,, I'd ignore her in a polite manner,, all while wanting to tell her to take a hike & look around at the real world & what is shown daily in many, many more venues.
The scene in question was an honest scene that had ZERO sexual overtones. It was a man taking a bath & suddenly discovering he was not alone as he thought. Heck,,, in my business,,, I had a woman taking a tub bath,, felt/heard scratching in the tub,,, vacated the tub,, all the way to the outdoors,, butt naked. An honest reaction to fear or whatever. (Turns out a possum had a nest in the hollow space behind the tub,, not any access to the home.)
I also had a girl I dated over 25 years ago,,, who got pretty upset because of a brief nudity scene in a movie,,, being shown in my home,,, on HBO. A Steven Segal movie,,, where a girl was topless,, and her bare breasts were shown briefly,,, and then she was shot & killed as she was a "bad" girl. My son,,, who was about 10 at the time,,, was watching the movie with all of us. (None of us had ever seen the movie,,, so we didn't know about the scene.
As a parent,, I felt if I made a big deal about it,,, my son would want to get more inquisitive about why I wouldn't let him watch the movie. My girlfriend felt I should have immediately stopped him from watching the movie. I felt that my response created a lesser impact than if I'd gotten upset about it all. Turns out,,, she'd been studying our relationship with an eye towards the future,,, and she wanted another child. She felt my parenting wasn't to her standards,,, and would cause us conflicts. While we remain friends,,, (because she was honest,,, & calm in her explanations,,, and had her beliefs,,,) we went our separate ways.
Parenting is done differently all over the place. Defer to the parents,,, apologize if they felt offended,,, but try & NOT make a bigger deal out of things than they are.