I wouldn't be surprised if GF had been trying to push through despite the pain, because even if neither BF nor his parents explicitly told her to, there's general cultural pressure, and an idea that it's weak or childish to not do things because they hurt. (Maybe it is weak: weakness is not necessarily a character flaw, sometimes it's just a fact about a person's body, like being tall or having green eyes.) Or, along similar lines, that she felt that it was inappropriate to talk about being in pain, even if she was having to stay in bed because of it.
We don't know why BF's mother was asking intrusive questions about GF's health, but it might have left GF feeling judged, as if she had to produce the "right" answers in order to have her disability taken seriously.
I generally think that what I need to know in order to make accommodations is what the accommodations are. Sometimes the symptoms are relevant; the underlying diagnosis is less likely to be so. A good friend of mine happened to mention, the last time I visited her, the physical issue that is the cause of a significant part of her chronic pain. I hadn't asked because it didn't matter and didn't really feel like my business until she chose to make it so. What matters in my friendship with her is that she sometimes needs to stay in bed because of back pain, not always predictably, and she often uses a cane to walk, and is never going to run for a bus, and may say "Tea Drinker, slow down" if we're walking together.