Well I'm sorry to tell you but if she's not interested there probably isn't much you can do except maybe try & get her into a threesome with a friend she trusts to get her feet wet. But you don't want to push her into it. I've seen too many try that and the only outsides involved were the judges & lawyers at their divorce. But good luck.
'Reminds me of a party at a friend's house who lived out of town. Everyone had left except for four or five guys and my wife was dancing suggestively for them having no idea she was my wife. Eventually they started feeling her up as she rubbed up against them. Soon they had her top off exposing tits and she went on & slipped out of her skin tight jeans. revealing her sexy 5-8, 110lbs, 34D-24-35, red hair & matching bush with piercing green eyes. They were servicing her in no time. And at her request they all shot their cum on her big tits. They were shocked when we were getting ready to leave together and one guy said he didn't know she was my date. I laughed and said no she's my wife, then said but don't tell my girlfriend and left them confused.