his mother was no stupid woman; she could roll an R like a queen. (lines 58-59)
The phrase "like a queen," implies royalty, which is kind of what Trujillo imagines himself to be. It's a grotesque parody, of course, because he's not royalty – he's a vicious dictator. But, in Trujillo's head, his mother (despite her half-Haitian heritage) is infinitely superior to the people he has working in the cane fields outside the palace. The implied contrast is that the Haitians are both poor (true) and stupid (probably not true, but this is how hatred forms, as we'll see).