All honesty if you go in the well unprepared then you're basically screwed. Got me the first time (& a couple times after that too). I always stock pile Sacred Water long before I complet Restore The Temple cos I'm pretty sure that triggers the countdown to when Liandra will go missing. At which point you literally have no other resource for Sacred Water which is key to make pretty much every potion (bar like 1 or 2).
Best bet to get through on lowest resources is poison you're weapons, have access to HP potions, Mana potions & Energy potions. Lots of Bandages for inbetween the fights & potions to enhance yourself (Giants Strength, Agility & Stone Skin). I would also give poison for Elf's arrows when she joins. Also Cure Poison to avoid infection from bats or mushroom spores.
Best strategy is all that with the added benefit of Familiar to help with HP potions (if she can survive each fight), Wither spell to weaken them & always target the ones with no weapons (white hair with a glowing hand) & the Great Grumpkin first cos they are the lighting guys. Try to pick you're fights. Staying to the Bottem wall let's you avoid the 2 Grumpkins past the dam if you're quick.
Sadly sounds like you have to tough it through & pray yo the number gods OR start from an earlier save...