Water weapons can dispel the flame spots, so do puddle pods and for some reason crystalburst.
Fireproof mantle makes her nova laughable and if you have it, heat guard makes a massive difference.
If you don't have a fireproof mantle, well timed dives can minimize the damage her nova does, or you can run into a flame spot, this will knock you down, you can then stay down and be safe from most of the damage. Do note that this will still damage you some, so if you have low health it's safer to attempt to dive through it.
Attacking her head is relatively safe as her flame breath attacks have a big tell, just be wary of her claw attacks and dash attack.
It should be worth noting that her wings take the most cutting damage. If she's downed and you're using a cutting weapon, you should attacking the wings, if you're a gunner cutting ammo does a lot to the wings, and you're not restricted to topples to deal big damage to the wings so go crazy.
Flashing her tends to force her nova. If you're playing solo you can run and flash her while running away. Most of the time this gives you enough time to get away from her nova. If you plan on doing this in multiplayer make sure you warn your teammates.
She has almost no attacks that hit her back legs, so that's a very safe place to attack. Just note that cutting damage is very low back here.
You can actually get gems from shinies so if you're grinding go for every shiny you see.
Those are just some tips for everyone. Feel free to add more in the replies, so everyone can benefit. Preperation is key when it comes to lunastra!