I would recommend the Lauterbrunnen area for the beauty of the valley and the great views provided and there is more there to see than the Jungfraujoch trip. We also took my 80 year old Mom to the area. We stayed a couple of nights in the Valley Hostel - my Mom and I stayed in a private room and the kids stayed in the dorm side - best value for the area. The Coop is right across the street and we cooked meals there.
The trip to Shilthorn is one option. Take the cable car from Lauterbrunnen to the Lauterbrunnen - Murren mountain railway - great views. If weather is clear, cable car up to Shilthorn to the revolving restaurant. They have a great breakfast buffet.
My mom, while not on oxygen, did go to Jungfraujoch with us. The trip to the top in late July was extremely crowded. We immediately went to the restaurant, sat down and drank lots of water and had a snack before walking around at altitude. It was a sunny day, so we found for her an open chair outside overlooking the activity area while the rest of us walked the snow trail and slid around in the snow. She did fall in the ice cave, was not injured, but gave us a scare. Should you decide to go - I would recommend, if possible, taking the first train up (around 7:00 am) - the weather will be better and the crowds less. Any other time and you may find standing room only and for two hours, that is not fun.
If she likes to walk and can for an hour or so, the hike from Mannlichen to Kleine Scheidigg is very easy and slightly downhill. You can access the Cable Car from Wengen via Lauterbrunnen or from the Grindelwald side. I did this when my daughter was very young and it is very easy, many benches to stop for a picnic or rest. Restaurants at both Mannlichen or Kleineschidigg for a snack or drink.
We also took my Mom to Pilatus which she enjoyed as much as Jungfrau. The funicular ride to the top and the views of the Alps were great. She found a chair and spent her time watching the Steinbock on the rocks nearby and the paragliders.
Another option would be the Niesen. It's lower than the Jungfraujoch (about 2300 metres), but the view is stunning and there is a good restaurant at the top. Much less claustrophobic than the underground passageways of the Jungfraujoch.
Beautiful train ride via Luzern and Interlaken as well, it would make a really nice day out.
Or from Interlaken Ost station, take the pleasure boat to Brienz, and then the steam train rack and pinion railway up to Rothorn-Kulm.
There is a restaurant at the top and views of the Eiger, Mönch and Jungfrau. And MUCH cheaper!
http://route.search.ch/?route=brienz...nz&poi=verkehr
http://fahrplan.sbb.ch/bin/traininfo...urneyEndIdx=2& Journey time 60 minutes one way. No crowds!
If you are feeling adventurous you could take the cable car from the top down on the north side to the bottom at Sörenberg-Schönenboden
and catch the Post Bus to Schüpfheim and then the local train to Bern.
http://timetable.search.ch/brienz,ro...07%2F01%2F2014
Note all journeys are planned for 1. July 2014
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On another point, my OH made the trip up the Jungfrau and he said it was an absolutely nightmare because of the way that they jammed so many people on the train. For anyone without medical issues it was very difficult.
As others have said,on oxygen it is a no no.
With her health conditions I wouldn't take to the Joch either, especially not in peak season. It seems that every single Japanese, Korean and Chinese MUST have been on the Joch in August
I have a aunt in a wheelchair and took her with the Glacier Express from St. Moritz to Zermatt. Breathtaking scenery all the way and GA and 1/2 tax are valid as well. But you have to reserve places.
The other thing is the temperature. Even in the middle of summer, on a perfect sunny and still day, it was below freezing up there, and the ice palace of course is also under zero degrees. It is a long walk from the train to the various areas of the bullying, and it's cold.
Our family thought we were exaggerating a bit when we told them they would need full snow gear and waterproof shoes at the top....but we were certainly glad they did.
The ice palace has steps and is long and slippery. With the coldness, and the slip risk, would be uncomfortable taking an elderly person in there....
I am trying to think of a mountain that has only one cablecar up and down, or a train, or just really good views.
If you did not go to the thine falls last time, I would definitely recommend it, just organize some wheels or take the local train that stops at the high side of the falls, where you do not have to walk far for a good view, or get a taxi to drop you near the side of then bridge.
For views of mountains, my mum loves the trip to Chur. Or maybe one of the other tourist trains. I wonder also if there are any ice palaces that are cooled and at lower altitude....we saw one in Singapore!