My mother needs to be moved to an assisted living facility, but my father is still capable of living at home. Can we file for her based on my father’s service?

The veteran has to qualify in order for the spouse to be eligible, so no, you cannot file based on her need. However, a vet with an ill spouse can file for "Basic" Pension if all of her medical costs wipe out their monthly income. The application process is the same as if the veteran were filing for Aid & Attendance.