Sounds like your wife likes simple stuff, perhaps a bit sweet. Try dark or amber rum for her, with either coke, 7-up or gingerale. White rum is too blah, especially if you go with a cheaper variety. You could always try a flavoured vodka with tonic, or just spring for a nicer bottle, Greyhound or something to that effect.
If you're looking to drift into Scotch, maybe try a rusty nail to start. 1/2 Drambuie and 1/2 Scotch makes a nice lead into the harder edge that straight Scotch provides. I still really enjoy drinking them, in spite of being a Scotch fan as well. With Scotch, pay the price for something nice. You'll either end up in the highland or the islay camp. The islay is much smokier and peatier, not my taste. The Highland varieties are a fair bit smoother, more heather, less smoke. Cardhu is nice but at the high end, Glenlivet, depending on age, can be nice and cheaper (less expensive). Best to find a bar/pub/restaurant to try a few out before springing for a bottle. Surprisingly, I prefer a blended Scotch in my rusty nails, Johnny Walker black. It gives it a nice distinctive taste and doesn't seem like such a waste as pouring in a single malt.
Don't just mix whiskey with coke, do try gingerale, soda and 7-up/sprite, the difference can be quite nice. I think Scott (OCB) would suggest a nice Canadian Rye whiskey, but go with whatever you find tastes good. I've never been much of a fan of whiskey, but that's mostly a grade 11 story anyway
Dave's suggestion of a Long Island Iced Tea is something that should appeal to your wife a fair bit, the taste is well hidden. A substantial difference between Canada and the US is our restrictive liquor laws and prohibitive alcohol prices. I can make drinks that could kill you without you knowing it, as opposed to the more blunt US approach, though I will say Americans tend to have a bit more staying power with hard liquor and seem to appreciate the taste more in many cases.
Coolers should also appeal to your wife a fair bit, though again, Dave said so first.