Hi Jocelyn,
There is no chance for me to give up at all. 
As far as I know, there are no options to enter any date range in SWI2_ADM2. I simply checked the checkbox for Orphaned Items and found empty results.
I talked to my client as well and she said that she might be wrong. She daily gets many workitems and that's why she told me that she was expecting some more workitems that day. I know that' sort of weird but these guys are really new to SAP and so quite nervous about anything done wrong from their end.
Also, just to double check I got my ID deleted from DEV system and then recreated. And yes, I found all my workitems as it is in my Inbox. So, now I am pretty sure about the results when a user gets deleted from system.
I am trusting the system now and assuming that there were no more workitems for her. But in case, she gets to know about anything missed for her later on, probably then I will need to dig further. Currently, busy with many more after go-live hypercare activities.
Many thanks for your guidance.
Regards,
Richa