The reality is that she used such a service because she delegates such activities. To use a Trump answer, she hires people to do that. She doesn't approve every vendor, decide on every IT purchase. I can see the conversation now:
Abelin: Hilary, you have Debbie at the DNC at 10, Senator Sanders at 11, lunch with the President at noon and the IT guy needs 15 minutes of your time.
Clinton: OK, I can squeeze in the IT guy now.
Abelin: I'll send him in.
IT guy: Ms Clinton, I've order all the hardware for your office and put in the high speed network connection. What do you want to use for the email server?
Clinton: What are my options?
IT guy: You can use the State Department default email account or you can set up your own server.
Clinton: Which do you recommend?
IT guy: Colin Powel and Jeb Bush went the email server route. It gives you a little more control over your email and a few more options around creating accounts, but you'll have to pay for it yourself. The State Department account is free but you'll have to go through the help desk if you need assistance.
Clinton: Hah, I was on hold for an hour last time I called those guys! Do the server thing, send the bill to Bill.
I know Republicans imagine Clinton sitting in a poorly lit room wringing her hands cackling about how she will hide all her emails from the public, but just like Trump, she hires people to do that stuff. Is she still responsible? Sure. Does she personally investigate the background of all her vendors? Doubtful.