Have you tried cilantro? That's usually a favorite. Every rabbit I've ever had other than Nala has gone nuts for cilantro. She, like me, hates it (I call it "stinky cilantro" when I'm passing it out and always wash my hands right after). Turnip or collard greens would be another good leafy green to try.
When we got Harley Quinn and Barnaby, she was a smidge underweight. Barnaby, who she's bonded to, is a Californian (meat rabbit breed) and therefore more prone to obesity (and eats like a vacuum cleaner), so it's hard to feed HQ generous portions without him eating too much. At first, she snubbed my daily offering of a little chunk of fruit - I tried like five different fruits before finding one she would actually eat.
Sometimes rabbits learn to try new foods from watching other rabbits eat them. When I first started feeding rose petals, two out of four rabbits refused to even try them but came around after seeing the others gobbling up petals! Since you only have one rabbit, you can try being the other rabbit. Sounds weird, but sometimes it works. Lay on the ground with your rabbit so you're on their level, nibble on the greens you're offering and make happy faces and tell them how good it is. Repeat as needed. No guarantee it'll work, but it's worth a try!