Translation:The woman did not remember anything after the accident.
I actually found a great resource for this on a site where an Italian was asking for help translating. Here's the response:
Basically, "incidente" means "accident", where something like "caso" or "evento" would mean "incident". The response actually goes deeper and talks about how the term "accident" in English generally refers to something that happens through misfortune, while an incident often has culpability attached to it. The fun thing is that I found a lot of Italians asking about the same problem, because although it's a false cognate, it's a very subtle one.
That's the past perfect, not the past tense. You'd have to say "non aveva ricordato niente" to get that meaning.
This tense can only be substituted for the present perfect in terms of its literal meaning. The difference is that this tense is rarely used in conversation, and when it's used in writing, it tends to refer to a period in the distant past.
"Signora" is probably better for "lady," but that's when you're using it to indicate a level of respect/deference for someone's social standing. Translation is a little more difficult because it's rare for English speakers to differentiate between "lady" and "woman" in contemporary speech.
There's an extremely subtle difference between the reflexive and non-reflexive form of the verbs. The best summary I found was here: https://langsandlit.tumblr.com/post/146947201038/when-does-one-use-ricordarsi-di-vs-ricordare
Given that difference, the reflexive form doesn't make much sense here. "Ricordarsi" requires some kind of specific object, rather than a generic sense of memory.
There are quite thorough discussions here: https://forum.duolingo.com/comment/29471221 and here: https://forum.duolingo.com/comment/27272367 . I take nerevarine1138's point that there is a subtle difference, but CivisRomanus reports that they are often used interchangeably, so it seems a bit harsh that DL won't accept ricordarsi.