this is a settled case. You have to mention the end date as per the last working date being considered by company in the experience certificate. Leave taken due to illness and otherwise; a valid reason not been able t submit resignation should be a ground good enough to issue the experience certificate with last working date as date.
Yes, you are within your rights to mention the sabbatical leave if you wish to. But, if you ask me I would not do so. It will be unreasonable on my part, as it was without a choice employee had to go on extended leave.
Answer my question :What if she re-join again and works for 6 months or so, and then resign, What experience certificate will you issue.??? Will you still mentioned sabbatical leave??.
It's my opinion, that you must mention "Start Date" and "Last Working Date", as you would consider her for her full and final settlement, immaterial whether she worked or not.
11th May 2014 From Saudi Arabia, Riyadh