I read somewhere that they originally wrote this day's scene because they didn't know if she would renew. Now she appears to be on an extended vacation (in real life) according to an article I read.
So, maybe Ashley only hit the guardrail that Nikki was near, or maybe she wandered away injured and her memory gone. That would be a new concept.
So, Kimmie et al, where in the world is Nikki?