Yes, your Mother can qualify you to file as head of household and she can qualify as your dependent as long as you pay more than half the costs of keeping up the main home for the year and you meet the additional requirements for both head of household and the dependency exemption.
For her to qualify as your dependent, her gross income for 2016 needs to be less than $4050. Her alimony is taxable income but I dont believe the social security benefits will be taxable. However, please review the publications that I have referenced as well as the FAQs and then make the determination.
