Have you tried sunfire+IBG Leona? Its actually pretty damn strong if you can get past super early game maxing Q first.
I think its better in the jungle so you can build Abyssal without being punished by lack of HP due to Cinderhulk+SotA. Abyssal alone puts her base damages back to her old values, and makes her do significantly more damage with what was added to her ult and the MR reduction. Grab Warmog's to ensure you have enough HP to go along with your resists and fill you out at 40% CDR, which gives you 33% uptime on your stun and practically a 30 second CD on your R.
You end up being able to 1 shot carries as essentially full-tank, and a stun to follow-up if you don't. Randuin's+Tabi to ensure you can kill them before they kill you, provided your team decides to sit around and do nothing. If you can start with E, you can kill them before they retaliate E->Q->R->Q->E->Q. Not bad for building basically tank.
The biggest issue with a bruiser Leona is early game. Top lane has too much bullshit for her to farm in, and jungle she's too punishable early on, although her clear-speed becomes pretty damn good after Cinder, and practically instant with sheen.