A lot depends on whether or not that other person is entitled to claim you as a dependent on his or her own tax returns. For example, a parent who provides all of the support for an underage child who lives with that parent is entitled to claim that child as a dependent, even if the child does not want the parent to claim her as a dependent.
On the other hand, if someone is not entitled under the tax law to claim you as a dependent then they cannot claim you, whether or not you consent to them claiming you as a dependent.
Based on your description, which is a little short on facts, you can certainly file your own tax return, and you must if you had income in 2012; however, if someone else was paying for all of your support, including your housing, then that person will probably be able to claim you as a dependent, which means that you will not be able to claim yourself on your tax return.
Finally, you don't say who this other person was who claimed you last year and prevented your mother from claiming you; if you weren't that person's "dependent" under the tax law, then that person could not legally claim you. To get the real answer to that question, however, would require that you discuss you situation in detail with a competent tax professional; any answer you get for free online is not going to be reliable.
My answer does not constitute legal advice and may not be relied upon by anyone for any purpose and does not constitute an attorney/client relationship or an offer to form such a relationship. This disclaimer is intended to be fully compliant with the requirements of Treasury Department Circular 230 and the terms thereof are fully incorporated by reference. If you wish to consult with me please contact me at dana@nytaxcounsel or visit my website at www.nytaxcounsel.com