Sorry to hear that your wife can no longer ride.

I'd guess that the bike's an '88 model from the decal style. Check the headbadge for a light, four-digit stamping. The first three will be the ordinal day of the year and the last the last digit of the year of assembly. For example, '1228' would be the 122nd day of 1988.
The bike looks to be in pristine condition, but, unfortuately, there is not much of a market for "mid-vintage/mid-level" Schwinn mountain bikes. It would probably bring around $150 or so.
Love the color though! I would think the new owner would be proud to have it.
Best of luck,
Bob