Here is what I'm using, It's what's working best for me after a few dozens hunts.
Phase 1, mantle On :
Rocksteady -> Tenderize chest/head + arms if possible
Fling shot x2 (stonethrower jewel so you can double wall bang, you'll have 5 rocks left and can chain the 2 as soon as she lifts her head up, timing is key : not too late so she turns her head/body, not too early so the fling shot registers)
Instant sleep her during her enrage roar if she's in a good position (access to head easily, in direction of the wall) or wait a bit for better position before sleep
Put bombs on head when sleep, grab crystalburst/red ammo to fling shot, and wyvernsipe for wakeup if solo or nothing better (GS/Hammer) then double flingshot
Sticky to head for stun, use cluster when KO/downed on the edge of the tail/mantle to avoid knocking down teamates that are hitting the head
Use Fireproof mantle as soon as the CC chain (4 fling shots) are done because with fire res at 0 you WILL get OS by the fire breath
You can use Para in phase 1 if you're alone to cluster or if you're the only gunner in the group (if you're two gunners maybe the other one will use para in 3rd area so I usually avoid using it)
Phase 2, Mantle Off :
Area 2, fling shot to enrage her + dmg, tenderize her head as usual, then use the boulder to knock her down, if everything has been going smoothly horns come out at this time, with 2 TCS it's like 4000+ dmg
I'd say wait for area 3 to fish for mounts and when her head is tenderized (airbone is really strong in phase 3 you can climb up the walls at the edge and middle and do a charged slash midair for 600-700 dmg) but it's my opinion, mounts in phase 2 are good if you need the damage to get to the 40% threshold obviously
Just beat her ass lol
PS :
You can switch out 2 attack jewel or the big attack jewel for 2 level of fire res for the range build, so instead of eating for elem res+ or counting on your fire mantle you can eat for safeguard, which is really good online ; I usually swap the jewels to avoid a 180 instant OS when playing with players because her comportement is unreliable.
I was initially playing with this build when the mantle was off : https://imgur.com/a/BjafFDk But I feel like Raw is much better as soon as a part is tenderize, I haven't done extensive testing though, so feel free to correct me on that one