Of course, she wasn't the first Secretary of State who preferred to use private email; Colin Powell did the same.
The difference is Colin Powell didn't use his own private server and had a .gov account. Hillary didn't. I'm pretty sure all government officials have used personal email at some time or other but none have had their own server.
It was a really bad unforced error by Hillary. She certainly should have known she would be found out. The good news it seems like it's a case of no harm, no foul.