Judging from your description that is an older 3.5gal/flush toilet.

Try an experiment. Instead of flushing in the normal manner put 3.5gal of water in a bucket and pour it directly in the bowl and see if it flushes normally?

If it flushes normally when you pour water directly in the bowl both the vent and drain lines are ok.

The problem most likely is that the water from the tank is entering the bowl too slowly, which is a very common problem as the bowls age.

Under the rim of the bowl there is a row of small holes where the water from the tank enters the bowl. As the bowl ages those holes become partially obstructed from mineral buildup or waste material from the bowl.

You can don a pair of latex gloves, then take a small diameter drill bit, just slightly smaller than the holes and go around opening those holes so the water can flow out quicker and that should resolve the problem.

Thanks Lazypup, that does appear to be the problem, it flushed normally from pouring a bucket of water in. I never realized a toilet could get clogged there, although it does make sense. Of course, I have never dealt with a 56 year old toilet either. We are going to attempt to clean it, as she is of the mindset that nothing should ever need to be fixed or replaced, hence why the bathroom with its pink toilet sink, and tub are original, along with almost everything else in the house..... You have been a big help, again, thank you.