Is it legal to have the other joint account holder claim all the 1099-div?

My mom and I have a joint brokerage account. She has no income but is the primary account holder. I put money into it to buy stocks that give out dividends, my mom then takes the entire dividends and uses it for her living expenses. Since she is the primary account holder, I'm told the 1099-div will go entirely to her.

Is this entirely legal?