Due to being a duel between the cultists, perhaps she could run an Archfiend deck? Or it could be based on The Wicked Avatar, whose attack points are always 100 higher than the highest monster. The Calculator ties in with this, making it so The Wicked Avatar always has at least 3700 attack. Combo this with Twin Swords of Flashing Light - Tryce and Shooting Star Bow - Ceal works too, since the cards decrease his attack, but he'll just regain the attack due to his effect. As he requires three monsters, the woman could have Scapegoat in her deck, using it to summon the Wicked Avatar, then summoning the Calculator in order to increase his attack. Using Double Summon, she can get out Hardened Armed Dragon then sac it for TWA, which would make him indestructible by card effects, which could make for an interesting play.
Further combos include:
March of the Monarchs in case she cant get out Hardened Armed, so TWA can't be destroyed by card effects.
Mystic Tomato into another level 4, then summoning another level four, XYZ into Master Key Beetle in order to protect March of the Monarchs and Pole Position to make him resistant to spell cards.
Double Coston counts as two tributes, have a decent attack for a level 4 of 1700, or Giant Germ, which deals damage when destroyed, and can summon another Germ.
Calculator increases attack for all level monsters he controls, so, his own level with The Wicked Avatars, TWA will always have 3700 attack, and even summoning another level 4 monster boosts TWA to 6100.
Edit: Whoops, sorry, got carried away. I used to play a TWA deck on YgoPro, and used the above combos to basically make him indestructible.