toilet water high in bowl
I am asking this for an 81 year old relative. When her toilet is flushed the water enters toilet from the tank normally, but it fills really high while swirling around, coming within about a half inch of the very top. It swirls around, and will eventually drain out, no gurgling noises, just a slow draining, but the bowl has always emptied with no problem. The bowl stays at a normal water level. It has done this for at least a few years that I have witnessed it, but she says it has been that way for years, and has had a plumber check it years ago, and he said that is how it's supposed to flush. Just this week, she said not everything is going down when flushing, prompting a second flush. Is this a vent problem, or a drain line problem?
Other info... This is a ranch house and was built in 1955, she has owned it since 1984. She is 81, and the only occupant of the house. It has always been on city water and sewage and it is the original pink toilet that has the problem. It is on the main floor. All other drains (bathroom sink, tub, and kitchen sink, which are all original piping) in the house run normally, and there is a toilet in the basement that flushes normally. The basement toilet was added about 20 years ago.
Any ideas are appreciated.