But it's not ambiguous at all! At least - she was violently attacked by her husband, and Trollope's description of her injuries accords pretty precisely with the results of an untreated fractured hip. From wikipedia, about untreated hip fractures:
"On examination, the affected extremity is often shortened and unnaturally, externally rotated compared to the unaffected leg."

I think her absolute refusal to self-pity is amazing - also her deft redefining of herself as unable to walk, and needing to be carried everywhere by two or three attendants. She can walk, of course, but it would be with a pronounced limp, which she knows would be seen as pitiable and ugly, and she just doesn't choose to be seen that way. It's this, not her premarital sex, which makes her such a morally defiant character in the nineteenth-century world - all the right-thinking invalids try as hard as they can to be mobile, even cheerfully calling for amputation and a wooden leg, like the girl in Pillars of the House.
Trollope of course admires her greatly, even if he thinks she's as damaging and self-destructive as all the Stanhopes.