Yes, your mother can receive both social security and VA Disability Pensionat the same time. To qualify she would have to be over the age of 65 and not remarried. The purpose of the Non-service Connected VA Disability pension benefit is to supplement low or no income veterans and surviving spouses as well as those with high monthly out of pocket recurring medical expenses, it's possible to qualify for up to $1057/month depending on what her needs are.
Currently, the basic pension amount for a surviving spouse who has not remarried is $7933.00 annually which places mom below the basic pension by $133.00 since her income is only about $650.00 per month. In the event that her income is further reduced by the monthly deduction from her social security for her Medicare Part B premium of 96.40 the VA Basic Pension would supplement that expense as well to bring Mom to the basic pension amount set by congress. Without knowing for sure what Mom's asset situation is, for the purpose of this answer, I considered there to be no assets.
The basic pension is the first tier of the VA Disability Pension. To qualify for either the second tier: housebound or the third tier: aid & attendance mom would have to provide the necessary documentation to indicate the care services are needed and proof that they are recurring monthly expenses.
It is important to note that VA Disability Pension Benefits are non-taxable, but are factored as income for purposes of other federal benefit programs such as Medicaid.
I suggest completing a free prequalification questionnaire for review by a veteran benefit consultant prior to applying for VA Benefits.