If she changed her actual rate plan then yes it renews the contract but the upgrade tenure doesnt reset so if she was eligible for upgrade then she still is and can still get the discounted price unless she switched to a value plan. As far a contesting it months later I can't say
The answer is yes, currently for all individual accounts, a rate plan change would require a new contract. Also, I can tell you that during a rate plan change you go through an electronic tool in which you enter your phone number, Listen to the contract, And press 1 to accept or 3 to decline. This is the required process for any contractual rate plan change, and she would have had to complete that process before any plan change would have been made for her.