is it possible for a 19 year old to rent an apartment by herself?
Absolutely! In fact, once you turn 18 you can get an apartment legally, because you are legally old enough to enter into a binding contract. Also, fair housing prohibits a landlord from discriminating against you because of your age. (Once you are legally able to enter into a binding contract.)
Keep in mind that as a first time renter, you may have to pay a much higher deposit or get a co-signed/guarantor.
Depending on where you try to rent and/or from whom, there are several things they could look at to make a decision.
2. Income - usually need to make 2.5 - 3.5 times the monthly rent
3. Previous rental history
4. Employment stability
I can tell you with the company I work for, we have rented to many first time renters. Please do yourself a favor, and stay responsible. Don't use your own place as the time to break all the rules. It will come back to bite you.
I think it's great that you are already planning for your future. I wish you the best of luck!