You do not allow someone to claim you as a dependent. They can claim you as a dependent if you meet the requirements to be a dependent either under the Qualifying Child rules or the Qualifying Relative rules.
Click on My Info on the left side of the online program screen. Edit your personal information and select that you can be claimed as a dependent.
Did you file first and say that no one else could claim you as a dependent? If so, you have blocked your mother's ability to e-file this year. If you filed a return that the IRS accepted, then your mother will have to file by mail.
When your own return has been fully processed, you will have to amend it. When you amend you will go to My Info. Click your name and go through the screens to the question that asks if you can be claimed as someone else's dependent. You need to say YES. Do not amend yet. Wait for the IRS to process your return. Your parent does not need to wait for you to amend. They can mail her return whenever they are ready. Waiting will not help them.
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-a...