Twice I fought Shiva. The first time I got her to almost half her hp. I was SMN/BLM, and didn't have enough healing potions

I also fought her on Firesday. The 2nd time I went SMN/RDM (so I had the option at least to heal myself) and brought even more potions. But this time like a fool I didn't do it on Firesday, I did it on Earthsday. The second time I was beat bad.
Now both the times my Summon skill was low, 46, and at lvl 20 I thnk the cap is 63. So next time I do it, I'm making sure it's Firesday and my Summon skill is capped. But anyone have a suggestion, go RDM or BLM? How many potions of what, do you think I should bring? And does anyone have any ideas on some tactics? Run around, etc.. lol
EDIT: Nvm, I found a very good strategy already


Azuth
RDM 75/ NIN 70/ SMN 39/ WHM 38/ WAR 37/ BLM 37/ THF 15/ SAM 11/ BRD 8/ RNG 2
HNMLS: Ex- Assassin
Dynamis: Ex- DynamisBums, Ex-HydraCorps
LS: Densetsu, OrdoDraconis