When my parents were growing up, not wearing black was starting to become acceptable, so long as you were wearing 'Church clothes'/Sunday best.
But these days, a lot of people - young folk especially - don't actually own church clothes. My church is quite casual; jeans and t-shirts are the norm. That means that teenagers are even less likely to have the sort of clothes you'd traditionally expect available. If my understanding is either my best clothes or my church clothes, I'm going to look terribly out of place - but my parents certainly never thought of advising me that I should wear my business attire to a funeral (I had to google that when my grandmother died a few years back).
When I was in high-school, my friend's grandfather died very unexpectedly. Being from a non-religious family, she didn't actually have any 'Sunday best' clothes, couldn't afford to buy her own clothes right then, and her parents didn't have time to go shopping with her with traveling for the funeral. She wore her school uniform because it was the nicest clothes she had. Her (private) school uniform was a maroon blazer, white blouse with maroon scarf, and a maroon skirt, that was a little too short because she'd been shooting up like a weed and parents don't usually consider you'll need another size up a month after last buying it.
(Bolding is mine above.)
That's what I was thinking of when I posted earlier that I suspect that the prom dresses may have the best those young women could do on short notice.
I've posted elsewhere about one of my sons who attended a very casual church. When he was in high school he did not have any what I would call "dress clothes" that fit him. We had stopped selecting his clothes for him a few years previously, and he selected only clothes he'd wear to school or church - and at his church the teenagers wore t-shirts and jeans.
My son had an appointment for a in-person interview for a college scholarship program. The instructions he was sent said he should wear his "Sunday best", so he planned to wear jeans and a t-shirt (which were
his Sunday best that were appropriate at his casual church). I tried to suggest that he should wear what a traditional older person would think of as Sunday best, but my son was a very unyielding sort of fellow and he was sure
I didn't know what I was talking about. (He did switch from jeans to khaki pants, but he still wore a t-shirt to the interview, because that was his Sunday best and he couldn't imagine the interviewers meant anything different.)
Well, when we got to the interview building, it was full of teenage boys and girls all dressed in dressy clothes. My son and one other boy were the only ones in t-shirts; all the other boys had shirts and ties and dress slacks, and many wore suits.
I kept my mouth shut, and a few minutes later my son on his own whispered to me that he had decided in the future he would always dress up for interviews. I think he learned a valuable lesson that day.
Getting back to the OP, is it possible that those young women realized that their clothes didn't fit in well at the funeral, and maybe the next time they go to one they may dress differently?