KELETSO THOBEGA A Botswana singer and activist who was raped three years ago launched a campaign on Friday to fight high rates of sexual violence in the country, saying the rape of her younger sister last month had spurred her to act. Refilwe Mooki, 23, who still suffers post-traumatic stress as a result of her attack, said the "Say No to Rape" campaign would push for harsher sentences for rapists as well as measures to support victims and encourage them to speak out. "Enough is enough. We need to challenge people feeling entitled to other's bodies and violating them because…