Congrats, you’ll have a blast with it. Your girlfriend is a keeper. If it’s the rod and reel combo you’ll also want to add backing, a 5 weight, weight forward floating fly line, a tapered leader, a couple of spools of tippet, and some flies.
Backing, check to see if there is any documentation with your fly reel telling you how much to get, but if not 50 yards of 20lb test Dacron or Micron should be fine, and leave plenty of room to fit your fly line on top. Cabela’s Prestige backing would be good, although I think it just comes in 100 yd spools, which will probably be too much for your reel to hold all that plus fly line. You’d have to guesstimate, or measure it off on a local football field, or tie one end to your girlfriend and have her run all the line out and walk/skip/run back to you. The loop between going away line and coming back line will be approximately 50 yds and you can make a cut there to fill the reel.)
Fly line- a moderately priced 5 weight Weight Forward fly line, probably labeled “5 wt WF-F”) like Cabelas Prestige (30 bucks), Cabelas Prestige Plus (also 30 bucks but a slightly better line than the Prestige IMHO), Cortland 333+ (their weight forward “rocket taper” is 30 bucks), or Scientific Anglers Air Cel (25 bucks for the light green trout line 5/6 weight forward floater)
Here’s a link that will take you to other links for the backing and fly lines mentioned:
Cabela's -- View All
You’ll also need a tapered leader and a couple of spools of tippet.
Tapered leader- For your first, I would go with a 3 or 4-pack of 7 ˝ foot long knotless leaders tapered to 4X for 9-10 bucks. There are many good options, but I would pick the same brand for both leader and tippet. Cabelas Leaders and Tippets (not fluorocarbon), or for a bit more the Rio Powerflex would be good choices.
Tippet attaches to the end of your leader at one end and to the fly on the other. You’d want to add about 1 ˝ feet of tippet to your leader, so as you change flies you’ll be cutting tippet instead of chewing up your leader. The “size” of tippet is measured by diameter, and you’d use smaller finer tippet with small flies, and thicker tippet with larger flies. A few spools of tippet, one each in 4X, 5X and 6X would be great.
You can find links here for tippet and leaders:
Cabela's -- View All
If you’re shopping in person, take your reel with you, perhaps they can rig it all up for you. If you buy the stuff on line, you’ll want some help with knots etc,. Here’s a link if you do it yourself:
Finally you’ll need some flies to hang 20 feet up in the trees as well as fool a few trout. A basic assortment like the 14 piece Classic Assortment (about 15 bucks) or the 35 piece Bantam Assortment (about 30 bucks) would be a good start
Cabela's -- Fly Assortments
Add a few extra individual Bead Head Woolly Buggers, black size 8. They’ll come in handy for smallmouth, and are a great fly for trout too in deeper water – pools in rivers and streams, and lakes/ponds.
Congrats on the fly rod and reel.