My Boss Took Away My Promotion Less Than 24 Hours After My Signing The Contract For It Due To Complaints From My Coworkers

So I work (worked) for a small business, it’s a non-profit children’s museum, it doesn’t even have an HR department. My mom is the general manager, but I earn my place and I’m shown the opposite of favoritism (unlike son of the director of the museum who doesn’t do his job at all but makes more than anyone). Well last summer I was put on a position called “float”, which is kind of like a team lead on the weekdays (our less busy days) who just oversees the other workers, distributed and covers for other people’s breaks, etc. I guess people complained about the floor managers daughter getting a good position so I was told I wouldn’t be put on that position for the time being. I was about to leave for college so I didn’t get too upset about it, I just kept my head down and kept working hard. Then, this past Thursday, I was put on float again and did a great job. My mom called me into her office and said she talked to the director of the museum who said that I deserve a promotion to official team lead and I could run the museum on my own. (Team leads are the sole managers on weekends. They open the museum, oversee the staff, take care of any emergencies, etc. they get a title bump and a pay raise but only on the weekends they are assigned lead). Anyway, the next day I’m not even working. I get a call from my mom who said that the director got complaints from my coworkers about the daughter of the floor manager being trained for float and team lead, and she apparently told my mom that it would be best that I don’t get the promotion anymore so as to not upset anyone.

Anyway my question is, is it legal to take away a promotion less than 24 hours after signing for it without even getting to prove I deserved the job? I’m not looking to take any legal actions even if there are options, I’m just really ticked off right now and I would like to know if im being legally screwed over or illegally screwed over.

BTW I quit. I turned in my stuff today with a resignation letter that I like to think was professional but communicated the fact that I’m ticked that they’ve played reverse-nepotism on me twice. There’s a lot of other things that they’ve done that constituted quitting but these were just the ones the ones that pushed me over the edge.