Do I hAve to claim the funds for the whole year if I am The legal guardian of my sister?I only have received income for her for 3 months. Someone else claimed her?

My 14 year old sister lives with me full time since September. I am legal guardian have collected SS benefits for her those 3 months. Someone else claimed her on their taxes, do I have to claim the whole years SS benefits or just the 3 months.

Get your taxes done using TurboTax

If the benefits are paid under her SSN, then they are not included in your return at all.  They would be in her return, but if that is her only income, she is not required to file a Federal return.