All of Shiva's abilities are magic attacks, and they have long range with mid~high area. She has no resistance to berserk, which can be easily abused to make her stop using abilities at all. Once she's down to about half of her HP, 3 more smaller enemies will spawn on 2 sides of the map.
The smaller enemies actually have some decent HP. They're easier to deal with if you are using fire damage dealers with area attacks so you can hit them together with Shiva. Otherwise, you might have to play around with their resistances since it's pretty high towards the ones they're strong against.
Recommended Units
Dedicated tank that's fire element, pretty much the closest thing to the ideal unit for the fight. Both of them can be the main tank and main damage dealer for the fight.
King Mont has some area attack resistance and LB can inflict berserk. Tidus is another alternative if you want another unit to inflict berserk since it can be quite important.
Shiva's "Shooting Hail" is an area attack that can inflict stop. This can be devastating if you don't have any ways to prevent or cure it. Ayaka's LB can cleanse stop and increase resistance to it. Otherwise, Frederika's TMR can nullify stop that you can equip to any other unit in your party.
Map
Reinforcements
Shiva Stats & Resistances
Max Level Stats
HP
34761
DEX
330
TP
241
Luck
242
AP
347
Move
5
ATK
745
Jump
4
MAG
930
Range
1
DEF
40
Bravery
97
SPR
40
Faith
97
AGI
100
Hate
0
Buff・Debuff
MAG Up, AGI Up, Accuracy Up, HP Debuff Res+999%, SPR Piercing Rate, Magic Attack Res Piercing Rate.