Can I claim my ? She is 93 and on a widows pension of $520.00 a month. She can't live alone with that nor at her age. Why shouldn't I be allowed a deduction?

my mom is 93, in June of 2018 she had to come live with me. By July 2018 I was forced to stop working to care for her. Her income is not enough for Nursing Home nor is she eligible for other care. Why then can't she be my dependent? She cant work nor can be left alone.  I was forced to efile without adding her