Stranded for first time today.....

Mother was driving car for the day. She went to market, came back outside and car would no start. Battery problem. She got a jump from a fellow diesel person (Ford Truck) and off she went. Obviously not alternator because she came home parked it, and when I started it, it fired right up. Could battery need to be changed? Its the original one that was with car.....my brother in law has a new battery I lent him What are some possible issues, and what would I need to check if my battery is going out the door?