If your Tax Return has already been e-filed and accepted by the IRS, you will need to wait until it has been fully processed and you have either received your refund or your payment has cleared.

Once your Tax Return has been fully processed, you can Amend it to indicate that you can be claimed as a Dependent.

If your Mom wants to E-File, she will need to wait until your Amendment has been fully processed.  Otherwise, she will need to mail in her Tax Returns. 

Check out the TurboTax FAQ below for details on how to Amend your return: 

https://ttlc.intuit.com/replies/3288565