I was talking with my mother on how it is haram to go to weddings with photography, music, women who don’t wear proper hijaab. She says that if the person is close to her, not going to the wedding could cause greater harm such as relatives being upset or being seen as rude, how can I explain to her?

And who said that if you disobey Allah and do that which angers Allah Subhanahu wa Ta'ala, no problem will happen between you and your cousins or your relatives? If it doesn't happen in this way, it will happen in another way, and it might be even worse. These things don't really prevent problems and bad things from happening to us; it's actually quite the opposite. All goodness is in the hands of Allah. So when you obey Allah, Allah bestows upon you, and when you disobey Him, you might get punished.