You could still file taxes for 2018 even if your mother claimed you (and you had earned income - you had a job). You just need to be sure to enter on your 2018 return that someone else is claiming you.
Your question got cut-off, can you repeat it please?
[Edited 2/10/20 | 2:55pm PST]
You don't have to file if you have W2 income under 12,200 but you can file to get back any withholding taken out in boxes 2 or 17. But you don't get boxes 4 or 6 back.
To file a separate return as a dependent you need to set up a new account separate from your parents. Online is only good for one return per account. You can use the same email address for 5 accounts. You can probably use the Free Edition or the Free File website
Https://ttlc.intuit.com/questions/1894512-how-do-i-start-another-return-in-turbotax-online
Be sure on your return you check the box that says you can be claimed on someone else’s return. If your only income is W2 and under 12,200 you do not have to file a return except to get back any withholding taken out.
You mother claiming you does not exempt you from filing a tax return. If you had less than $12,000 of income in 2018, then that is your reason for not filing. Check boxes 2 and 17 of your 2018 W-2 to make sure you were not entitled to a refund of federal (box2) or state (box 17) withholding.
Your post was cut off, so it's not clear what question you were going to ask. But be advised of two things:
1. Since you were under 19, in 2019, you mom can still claim you, no matter how much income you had; if you still lived at home (for more than half the year).
2. With the tax law change, effective 2018, most people will get the same refund whether they claim themselves or not. The personal exemption has been eliminated and the standard deduction increased. So, there's no reason not to let her claim you.