No. You will not be eligible to receive a stimulus check.
Part of the ineligibility occurs if you can be claimed as a dependent regardless of if you are or not.
As your mom could have claimed you, you would not be able to receive a stimulus payment.
Please see the link below to more details on who is eligible and who is not.
But should she have been able to claim me as a dependent if I filled my own taxes and claimed myself?
It depends.
They can claim you as a dependent if: