Mr DRILLER DrillLand - How to hurt Druaga in the Hole of Druaga?

In the Hole of Druaga attraction in Mr DRILLER DrillLand, how do you fight Druaga, the boss?

When you have fetched the key and unlocked the door, you enter a room where Tiara (Eguri), dressed as Druaga, confronts you. She hangs from strings and moves back and forth outside of your reach. I have managed to figure out this much:

• She has a red, green, blue or yellow halo surrounding her.
• Using the matching "Destroy R/G/B/Y" red dristone will damage her in addition to destroying blocks of that color. I think the damage is fixed, and it’s lower on higher difficulties and levels.
• After you hurt her, the halo switches color. I think the new color is random.
• Using a "Recolor R/G/B/Y" blue dristone will change her halo to the corresponding color in addition to changing blocks to that color.

So one strategy is to collect as many red dristones as possible before the fight, and hope that you have enough of them. I have beaten her on classic difficulty at level 1 like this. In theory, if you don’t have enough it might be possible to keep digging down to find more during the fight, but you seem to need a lot of luck.

I feel like I’m missing something. Is there some way to hurt her without red dristone? Or are you simply intended to scavenge as much as you can before starting the fight? I have tried breaking blocks when she is in contact with them, including blocks matching her current color, but it hasn’t seemed to do anything. I have tried drilling her strings or blocks in contact with her strings. Perhaps I need to do something at a particular time?