For your answer 2: My initial preparation didn't include her latest payslip until we got the mail. I intend to proactively provide her latest payslip to USCIS so as to avoid a potential RFE later. My main purpose of my questions 2 and 3 was that what can we do if USCIS does ask for RFE about her employment history, in particular, her final day with her employer.
Thanks again for your reply, especially in late night. It does confort us a lot.