Child support as a form of income?

[Bienes Raices]

I just met with a woman at the rental. Her source of income was SSI + child support. As it turns out, they did not meet my minimum income requirement (3X monthly rent), so they didn't apply.

I've dealt with SSI before but how do you get proof of child support payments? Is it considered discrimination not to accept it as a form of income? My only concern about it is that the father might stop paying at some point or fall behind.