A TurboTax Online account can be used for only one tax return. When you did your mother's tax return in the same account that you used for your own tax return, your mother's tax return replaced yours. Your tax return is now gone and there is no way to retrieve it. You cannot switch back to your own tax return.
You should have used a separate account for your mother's tax return. You can have up to 5 accounts with the same e-mail address.