iMessage

Her Samsung Tablet should not be able to see your messages from the Messages App. Only other Apple devices can do that.

If you are using another messing application such as WhatsApp or Facebook Messages for instance, she may be able to log in to your account for those service.

With that said, you can create a new Apple ID if you need to, and sign in with it on your devices, or change the password for your current Apple ID and sign her out it.

click here ➡️ How to create a new Apple ID - Apple Support

and here ➡️ Sign in with your Apple ID - Apple Support

Does she have access to your Apple ID? Do you see her devices in Settings ➜ Account ➜ Devices?

If so, then she has access to your calls and messages. You should not be sharing an Apple ID.