That's cold for a 92-year old.
But, heating oil for a trailer shouldn't be costing $3000/yr, it should be more like $500 unless Americans pay 6x as much as we do in Canada (and it's colder here). She should hire some kids to install plastic on her windows
while some may state that she may not have the $20-40 available to pay for the kids; many community organizations have volunteers to help with such.
Sheet of plastic (drop cloth) and duct tape $5. Some good hearted person that reads the sob story can give up Starbucks for 2 days.:whiste:
Depending on the size of the oil tank, it could cost $200-300 per delivery easily. However, as stated before by others, a little insulation and that should last a trailer for at least a large portion of the winter.