Did I ruin my mom's $100 straightener /:?

no. i had a ceramic-plated straightener, I used to accidentally straighten hair that was damp... it sizzled a bit, & was bad for my hair, but didn't ruin the straightener. Although, mine was $120, it was a Chi, and my hair wasn't that wet... but I don't think you broke it. A straightener that expensive can't break with just a little water.