My daughter receives my texts and vice versa?

I have an iPhone 6s and my daughter had an iPhone 4. Recently, I bought her the new iPhone 7. At the Apple store, the employees told me to enter an iCloud account into the iPhone 7. Since, she didn't have an account, I entered mine. Once we got home, we found out that she could see my texts and vice versa because we had the same id. I want to give her privacy, so I made her a new account. She entered that new account into her phone. But, we can still see each other's texts. I think that might be because her phone was set with my account so it doesn't change. I want to let her restart her phone with her own account, but I don't know how.

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