Forcibly question elf about earth magic, and it's potential benefits if used upon you (to improve/augment oneself). Barring that being viable, ask about any magics that could strengthen you.
Have Kobold priest present so that he can try to catch her is she attempts falsehood.
Tell her that if she cooperates, and can improve you, you will spare her life, and let her go free in exchange for services rendered (this being a lie). Make sure the priest knows the general plan here beforehand.
Make sure other golems are kept distant so they can't interject and ruin the charade.
Magic is a potent thing, it is best learned of.