The depreciation before the husband's death was buried with him (or more likely, cremated).  Stepped-up basis means forgetting about any adjustments before death.  In fact, it's not always "stepped up" -- if the husband had paid more for the property than it was worth when he died, her loss would be reduced from what he could claim, had he lived. 

It's really only six years you have to worry about, right?  She might have been claiming too little for depreciation, but since she (or her preparer) didn't know how to calculate it, she might have been claiming too much by not taking nondepreciable land into account.

And are there unused carryover losses, to be adjusted?  How much is saved, by worrying about amended returns and/or Form 3115?  Tomorrow may just be another day, to quote Scarlett O'Hara, but it's also the day tax returns are due.