I took my SO and future wifey on a backpacking trip a couple years ago, her first and at a time I was still trying to find my hiking philosophy and gear. If I knew then what I know now about going lighter, we would have had a much better time. Hopefully you can learn from my naivete.
We went to Henry Coe, famous for steep traverses. Not exactly heavy packs but we definitely could have been lighter. There were lots of hot, steep, and dusty parts of that hike, and we covered significantly more miles than I had originally planned, basically hunting for water in a dry environment. Suffer fest! My favorite picture from this trip is of her flipping me the bird, in a moment we were both hurting from sore legs and heat!
It was a learning experience in our relationship, and luckily her love of the outdoors only grew deeper despite my shi**y trip planning. I owe this to an awesome lake and morning swims, some really cool wildlife, luxury camp meals, and her being a bad-ass woman. Also, it really was good for us both to establish a common love of and respect for the wilderness, and I developed a more healthy respect for her abilities.
A few things I would have done differently:
- don't allow any novice to pack their gear independently. It may seem like you're being overbearing or controlling by saying no to all sorts of comfort items, but your experience and ability to keep pack weight down is really valuable.
- like other posters have said, carry the lion's share of weight and do the yeoman's share of work.
- plan even more carefully your route, water sources, elevation gains, and mileage. go for natural beauty, solitude, low bug factor, etc.
- invest in a pump, UV or gravity filter, my lady did not enjoy the taste of aqua-pure, and really who does?
- after your adventure, take her out for a stellar meal at a restaurant halfway between the trail and your home. This will become a tradition and great memory for you both.