Honestly, who knows. I doubt Castro personally did anything, but it could have been someone from the party or an enemy of Cuba, if indeed it happened, as I've also read elsewhere (from an interview with her I believe) that she had a miscarriage, so who knows. The details of her story have changed a lot over the years and between older interviews and then her more recent book, but the bits that stay the same are that she fell for Fidel, they had an affair, she tried to kill him, he gave her a gun, she couldn't do it and instead they made love.