She can use your account, but (personally) I would make an account for her and then link the tickets to both accounts. That way, if for some reason, one of you is having trouble, the other person can try to log-in. It hadn't really crossed my mind until my last trip when my friend couldn't log into her account (the app kept saying there was an issue with her account and it couldn't log her in) one morning. I had her tickets linked to my account and I was able to call up her ticket and she got into the park. It took a bit, but she finally got into her account (no idea what was the issue ultimately). So now I'm a fan of each person having their own account and linking the tickets.