The first "accessory" might be Derek Hansen's book, "The Ultimate Hang". It is now in its third edition, but the 1st edition (Used) is pretty inexpensive and covers a lot of camping ideas for both gathered-end and bridge hammocks. The newer editions add more info about specialized systems, like the Amok and Haven designs.
A "must have" is to keep the goal in mind. Comfort. You get a flat lie, not by stringing the hammock tight but by having enough sag in the hammock body so you can turn a bit diagonal to the hammock center-line. For most people, that's hanging the hammock so the ends are about 83% of the actual physical length apart. For the usual 11 ft camping hammock, that means the ends are about 9 ft apart when hung. You also raise or lower it relative to the ground, so when you get in/out, you can just plant your feet on the ground and stand up, like getting out of a chair.
Two other measurements that get you close to that "apart distance" are to see that the hammock suspension angle from the tree is about 30° (or 60°, depending upon which angle you are measuring). Another way is to make a "gun", raising your thumb and extending your index finger. With the top of the thumb touching the hammock suspension, the strap should just cross the tip of your index finger.
Now this is an important point - these numbers are not precise. They are "iffy", "sorta", "about", and "ish". The goal is comfort. The "number" gets you within a range that most find comfortable. The goal is not the number itself.
Next - before she heads out, she should have some experience setting up at home. Either that, or bring a tent as a backup. The first night out in a new location, especially outdoors, is often a tiny bit disconcerting for many folks. Add to that the newness of a hammock, and the night might feel ... weird.
It takes a day or two for the body to learn the hammock is not a bed. Muscles need to learn that they can relax into the hammock body, and the pressure points that develop in a bed are not there.
And she should make sure she has sufficient insulation under the hammock - either with an underquilt, a pad in the hammock sleeve (if a double-layer hammock) or in the hammock bed. All these things can be tested at home before starting on the trail with a brand new sleep system.
Note that I haven't mentioned a tarp. This is not the place to completely duplicate all the information available on YouTube videos, posts on other hammock websites, and Derek's book.
Your avatar area doesn't show where you live, but around here, we are at the cusp of winter. Nighttime temperatures are in the high 20s. That adds another dimension for a "beginner". And you say this is her first (real) camping trip. In my opinion, you are putting too many "firsts" on this trip. It's almost a recipe for disaster. When I go out, I almost always make some mistake. Over time, those mistakes have moved into the realm of "mildly inconvenient". To make a "mistake", miles from the trailhead, in sub-freezing nighttime temperatures, with no Plan-B, would be ... unpleasant.
T'were it me, and it was my sister, and we weren't fighting about something, I'd have her come over and set up/take down her tarp and hammock about five times in a row. Kids today don't understand that. It's like in rock climbing, where the guide classes had us tie a specific knot over and over so we didn't have to think about it. Or back in school, in the olden covered wagon days, where we solved quadratic equation after quadratic equation, until we knew what to do just by looking at it. Nike's "Just Do It" and Apple's "You don't need a manual" might have made for successful marketing, but it also instilled unreasonable expectations of expertise, which could be deadly in the wrong environment.
Is "hammock kit" the British "kit" that's a collection of gear? Or is that like a RipStopByTheRoll "kit" that provides the material and sewing instructions for a hammock?
