Well I am not quite sure where to begin: Do you have Level 58 Gear? If not get that or Waterworks gear to start with. Also chceck you ring, amulet and athame to make sure they are the best you can get.
For this battle you should definitely have all of your Ice to fire prism spells and Ice shields Loaded (these you can dump some if they all come up too early). Load at least 5 ice blades & 3 Elemental Blades. Have some healing spells in reserve, but no so many that they get in the way of getting your attacks off. Don't load Frostbite and Snow angel they are not useful for this battle. Use a fire wand/sword. Feint is a big help if you have it. If not get a treasure card feint at the bazaar. A blade treasure card is helpful too (Ice, Balance or Dragonblade)
Place your first convert on the minion (Kill him first), use a second if it comes up in your deck on the boss. But the first attack is about the minion so don't wait too long on a second convert if it doesn't show up. Load at least 2 blades and then Frost Giant with a Gargantuan card. After the minion is dead, shield and then heal some if necessary. Make sure you have a convert on the boss and Blade up (2X) again (or traps), then Collosus with a Gargantuan. Repeat if necessary.
Obviously you can tweak this strategy any number of ways. In general, Kill the minion, protect yourself, setup for a BIG hit on the boss.