I can't say for sure what your instructor meant, but most likely you are correct in that she only wants you to send her messages through Canvas InBox (also sometimes called Conversations). It's a pretty simple system to use and I've included a link to the guide pages below if that helps.
Hello email@example.com Welcome to the Canvas Community. Thank you for posting your question. Canvas does not have e-mail. In Canvas you will find the "Inbox" which is the messaging system to communicate with your instructors and other students in your courses. You cannot send messages to your family and friends via the Canvas Inbox because, more than likely, they are not enrolled in the same courses as you are. However, if you send a message or receive a message via your Canvas Inbox, you can get a copy of those messages sent to your e-mail address(es). This is accomplished by your "Notifications" screen via your "Account". You can choose how you want to be notified about various things in Canvas...and you can further select the frequency of those notifications. So, for starters, if you want, you can add an additional e-mail address, phone number to receive text messages, etc. by following the steps in these Guides:
Once you have added a contact method, then you will see a column appear on your "Notifications" screen for each of those that you added. You can set how frequently you'd like to receive notifications or each row on the "Notifications" screen. For example, if you want to receive a copy of a message you received in the Canvas Inbox to your e-mail address, that would be the section under "Conversations". Refer to this Guide for additional information: How do I set my Canvas notification preferences as a student?.
I hope this information will be of help to you, Lexi. Please let Community members know if you have any questions about this information.