Since it looks like you are using Sage 50 Canada, I am going to move your post to that Support Group so that other users of this software will see it and can offer you their thoughts and insight.

Thanks,
Derek

Unfortunately, there is no nice answer to this one.  Sage only allows entries in the fiscal year containing the current session date, and the fiscal year immediately prior.

You have 3 choices, none of which is very nice.

CHOICE 1:  Print a 2016 trial balance, income statement, and balance sheet.  Open the trial balance in Excel, and keep track of your 2016 journal entries using Excel.  Once you have final 2016 numbers, enter a summary journal entry dated January 1, 2017, to record all your 2016 items.  Be sure that all of your 2016 entries to income and expense accounts are posted to Retained Earnings, rather than to the income or expense accounts in 2017, as otherwise you will be double-counting these items.

CHOICE 2:  Obtain the client's backup from immediately before she changed the session date to 2018.  Use this backup to create a spare database, which you will use just like the Excel sheet in choice 1 - make whatever 2016 entries you want, but realize that they cannot be automatically incorporated into the 'live' database.  To incorporate them into the 'live' database, you will have to do a January 1, 2017, journal entry as detailed above.

CHOICE 3:  Obtain the client's backup from immediately before she changed the session date to 2018.  Use this backup to create a new 'live' database.  Do whatever entries you need to for 2016 and 2017.  Double check your work for 2016.  Then roll forward to 2018.  Then RE-ENTER ALL ENTRIES THAT THE CLIENT HAS MADE INTO THE LIVE DATABASE AFTER MAKING THAT BACKUP.  These entries will be all of the 2018 entries, and possibly some 2017 entries.  To find the 2017 entries, check the highest 2017 journal entry number in the database the client already rolled forward, and compare it to the highest 2017 journal entry number in the backup.