This may be the case that she has either:
- Saved her username and password to the computer, or
- If your email address is linked to your mother's account and that's your username, that may be the reason for you logging into your mother's account.
Not to worry. If logged into her account, go to My Account > Save & Sign-out. This will giving you the option to sign back in, and you can enter your login information.
However, if the email address is the same in both accounts, here's how you can verify the usernames associated: https://ttlc.intuit.com/replies/3302270
