What is Laura’s mysterious mental illness past?

There are references to Laura having had a mental illness, but we don’t know details. Laura tells sister Katy: “They’ll look at my medical history and they’ll call me a hysterical mad woman telling lies about the hero surgeon.” This suggests mental illness in the past – but should this matter? She also fears she will not be believed because of how much she drank. Even her sister asks how much alcohol she’d had.