This is a strange one, but according to the appendix in the OHOTMU HC it's considered canon, and it does have an original illustration of Heather by Bart Sears:
http://www.gamebooks.org/show_item.php?id=1715
Marvel Super Heroes Game Book: Wolverine - Night Of The Wolverine
(The US one is listed as #3, the Uk one #4; both with slightly different variations of the same cover.