Rebeccanne

Maybe it's my accent, but this sounds much more natural than Rebecca-Anne. If I met someone named Rebecca-Anne, it would be very difficult to pronounce both "a"s and it would require consistent effort. I would naturally contract both the "a"s and kind of stretch them out to show they're both there, rather than pronounce them separately. I don't think Rebeccanne is the prettiest name, but it's easier to say than Rebecca-Anne.