Yes, you can still file your own Tax Return if your Mother has already filed and claimed you as a Dependent.
When starting your return, be sure to indicate that you are being claimed as a Dependent.
As you walk through the TurboTax interview process, you will need to answer "YES" to the question "Someone else can claim me as a Dependent" and "YES" to "and this person will claim me on their 2018 Tax Return".
