Damage from flat iron ?

I went to the salon to get my naturally straight hair trimmed because my mom said I could use one. After they blow dried it my hair looked straight already but my hair stylist said she wanted to flat iron it to make it look shiny. So I went along with it. As she straightened it I heard little ripping sounds but I put it off my mind and my hair looked great afterwords. Then when it came time to wash it myself, I had flyaways in every direction from both my roots and ends that weren't there before. I thought straightening your hair ONE time isn't suppose to cause damage especially if it's done by a proffesional? And she put protective products and did it just the way I've heard you're supposed to do it in sections? Now I have to dump 3 leave-in products in my hair to smooth out the flyaways. I know I have thin hair but the damage she did is ridiculously bad (looks fluffier and dryer too).