Melting the witch is very satisfying. Keep trying.
If you're just wanting to enjoy melting her, and don't care about the score in the mode, then just find the 1-2 shots that are your best and safest shots and shoot. But if you want to jack up your melt the witch jackpot, then focus on the white ones. Keep in mind that you cannot just shoot the spinner from having two balls cradled on L flipper, backhanding one into spinner, Rinse and repeat... because that will penalize you with no hold flippers for the rest of your ball.
From WOZ rulesheet: (credit to Scott Tiesma)
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For the lit shots only 4 hits are needed. The eligible shots are Spinner, Left Orbit, Right Orbit,
and Throne Room. Each shot starts out white and turn red if you hit it. A white or red shot will
count towards your total of 4 but each white shots doubles the jackpot and red shots only add
to the base value (which starts at 6250). This means that getting all 4 white shots to turn red
would make the jackpot worth 100,000 points.
If you Liquidate the Witch you are awarded points based upon what white and red shots you hit
and a timed “Ding Dong the Witch is Dead” 4-ball multiball starts. White/Green shots start out
worth 5000+ points but count down during the multiball. The timer countdown is only active
while flippers are pressed so this can be extended by not holding flippers up and not cradling
any balls.
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Rule sheet located at: http://papa.org/wp-content/uploads/WOZ-Rulesheet-Version-1-26.pdf
Battle the Witch section is on page 21.