If she has other significant health issues she may not be ready to endure surgery.

There are 78 yr old ppl who are vigorous and healthy, others are very physically impaired by illnesses by 78. My MIL passed away at 70, but she was an "old" 70. If you met her you'd have thought she was 80+ and going downhill quickly. Yet my parents are healthy at 88 & 81 playing golf, etc. If either of my parents became ill and chose not to pursue care it would be difficult, but I'd understand (my brother would struggle with that though).