If your girlfriend is like most women, she'll want to feel comfortable, look hot, and not be ground into the dirt by an overzealous boyfriend. Your first priority is to find a beautiful, mellow hike—try to avoid climbing 3,406-foot Carrauntoohil on your first day out—and surprise her with a post-hike picnic of fresh fruit, artisan cheeses, a hand-made-by-you baguette, a bottle of wine, and something chocolate. That will ensure that you'll hook her on hiking for good.
As for gear, if she takes to it, you'll want to outfit her in socks, boots, shorts, pants, base layers, jackets, hats, packs, sunglasses, and poles. But first: Find comfortable shoes. Unless you'll be hiking for days over rocky, steep, uneven terrain, I suggest you start her off with something slightly less intimidating than a full-fledged leather hiking boot. On shorter outings, I hike in a lightweight trail-running shoe like the XTerra XR1.0 ($95; xterrafootwear.com). Designed by former Nike employees for XTerra racers like Martina Navratilova (yes, she's crossed over to adventure racing), the XR1.0 has a sole that loosely mimics an animal's paw, giving it great traction, stability, and support. It may look like a running shoe, but the XR1.0 has extra armor with a carbon rubber toe, forefoot rock plate, and an almost indestructible I-Beam arch shank. Plus, it fits my long, narrow foot, has a webbed nylon weave for maximum breathability, and comes in both pink and orange.
Next on your shopping list should be a performance layer that wicks sweat and will keep your girlfriend cozy. Icebreaker's brand-new 260 LS Express Zip ($120; icebreaker.com) in black looks sleek, feels great with its fine merino wool knit, and is beautifully form-fitting. Designed for running, and, thus, working up a sweat, the natural wool fiber automatically controls the body temperature in all climates.
Since you're from Ireland, where I'm assuming you'll be doing most of your hiking, you'll need a waterproof shell. I like Eddie Bauer's ultra-basic, but highly functional BC-100 jacket ($129; eddiebauer.com). It's waterproof, breathable, and scrunches so small that it takes no extra space in your pack. Plus, if it turns out that your girlfriend loves hiking, the BC-100 has a hood that accommodates a helmet for your next couple's sport—climbing.