Mom faking -- How should I deal with it?

My husband and I are retired. We put our home back east on the market and moved to AZ in late 2007 to look after my very elderly parents in their home. Dad passed in 2009, our home sold later that year, and in 2010 we bought a place in AZ. Parents' home is in the desert, we wanted to be able to do outdoor activities so bought in a cooler area, which is a 2-hr drive (one way) from parents' place. Since then, I stay with Mom at her place to look after her 24/7, and husband stays at our place.

Mom is 95 and although she had a round of medical problems for most of a year during 2013 - 2014 (pneumonia twice, also diagnosed congestive heart failure, had pacemaker and vena cava filter put in place, and she has chronic kidney failure), for the last year she has been doing really well and no additional problems. She was put on oxygen 24/7 a year ago, but for the last couple months only uses it at night because she didn't feel she needed it during the day -- and I agree, as her blood oxygen checks always range around 95 which is really good for her age. I think she was put on the 24/7 oxygen because doctors felt she would deteriorate what with the pneumonia issues and congestive heart failure, but she has actually improved since then.

Prior to the hospitalizations, Mom was fine with traveling from her place to ours a couple of times a month for a 3- to 4-day visit with my husband, but in the last year and a half she doesn't want to do it. All that is required of her is to get into and out of the car, really, because for anything other than a distance of about 20 feet (she will walk short distances) she rides in her roller/walker. She spends her days in a recliner chair and reads or naps, only getting up to be taken to the bathroom and then to get ready for bed at night. The same routine is followed at both homes, she eats the same meals both places, etc.

Both my sisters live in this state, about an hour away from Mom's. They both work full-time. Roughly every 5 to 6 weeks, they will agree to come and look after Mom so that I can go visit my husband and he and I can have some "alone time" together and I can get a couple of days off.

My husband has arranged to fly to FL to visit his older son there for a few days. I asked Mom to be willing for us to go up to our place to look after things and pets during his absence, and she strictly refused to go. So yesterday I needed to go up there and get the pets and bring them to Mom's house -- she didn't like that idea either, but I told her it was either one or the other. She can't be left alone for 5 hours and there is no one I can ask to come and look after her for that period of time. So she had to go along for the ride. The plan was to drive the 2 hours up, relax there for about an hour and stretch our (my) legs, then drive the 2 hours back to her place.

The trip up was just fine until we got about 1/4 mile from the house. Suddenly she asked me if I had brought her oxygen tank, and I hadn't even thought of it because she doesn't use it now during the day. Immediately she said she felt like she was going to pass out. By the time I got to our house -- 5 minutes later -- she was moaning and whimpering. I told her it would be best for her to just stay in the car, and she agreed. I also told her that if she felt faint, to lean forward and put her head down, and she didn't do that.

My husband and I rushed to get the pets loaded up in the car while Mom cried in the front seat. My husband asked her twice how she was doing and she didn't even look at him and didn't reply. However, during this same time she carefully put her sunglasses in her purse and reached for Kleenex tissues without fumbling. Her color was good, she was not gasping for air, etc.

As I was pulling out of the driveway for the return trip, she muttered some "gibberish" in a high voice like a little girl and whimpered incoherently. About 10 minutes later she "came out of it" and asked if we got the dogs, and I said Yes. A few minutes after that, I had to stop for gas and she asked if I was OK and I said Yes and asked if she was OK, and she said she was "Fine." We conversed some on the drive home, with her apologizing and saying she was embarrassed she didn't acknowledge my husband. She maintained she didn't remember anything about reaching the house.

Here's the thing. As mentioned above, her house is at an elevation of about 2000 ft and our house is at an elevation of about 4000 ft. But we hit the 4000 ft elevation roughly 30 minutes into the drive, because of the terrain. And we stay between 4000 and 6000 ft for the whole rest of the 2-hr drive. She was not having any problem at all until we were almost within sight of my house.

Both my husband and I are positive she faked feeling "faint". She does have some passive-aggressive behaviors at times. Any ideas how to handle this?