Can my mother claim me as a tax exemption?

Yes, she can claim you as a dependent (not an exemption). And you probably are worth more to her in tax savings than you saved yourself. You can file an amended return and "unclaim" yourself. You'll owe more taxes (or get a smaller refund) and then she can claim you. (Requirements for her to claim you: 1) you are under 19 or 24 & a student, you lived with her for at least half the year, 3) she provided more than 50% of your support. )