The Night in Question by Susan Fletcher

Florrie Butterfield has cherished her independence all her life, so losing a leg in her mid-80s was devastating. Forced to leave the cottage she loved, she found a residential community in Oxfordshire that accepted people in wheelchairs, Babbington Hall. But just as Florrie has settled in, things start to go wrong. When the story begins, she is mourning Arthur Potts, a friend who fell out a window and died four weeks earlier.