In the game, you can see Rinoa wearing two types of dresses plus the astronaut suit (That, I'm too lazy to discuss). The very first scene where you see her would be the graduation ball. This is the ballroom gown. And the second is her normal battle clothes. One of the reasons why I like Rinoa is that her clothes are really cool and unique. I'll try to give a thorough analysis on her clothes below.
One thing I can say about this is that her battle dress is unique. Kinda bit weird since it looks like she squeezed everything from a dress to a skirt and shorts in it but still cute.
Rinoa wears a sky blue, ankle-length, cotton knit dress. It's open at the front and is has two stips that serves as clasps of the dress. On this strips are two blue buttons which then hold it together. At the back of her dress, you can see owl's, some say angel's, wings that also somewhat serves as her character symbol.
Rinoa is wearing a black body-hugging shirt under her outer dress. It might be the same material as that of her shorts. It has a spaghetti strap and a v-neckline.
I would estimate Rinoa's brownish-black boots to be six to eight inches high with a half an inch heel. It's made of leather and it has five shoestring holes, though she laces it only until the fourth hole. Her boots has this black strap with a silver buckle in the middle encircling it. It's added usually for stability. Now that i think about it, the boots of Ken, Aya and Yohji from the anime Weiß Kreuz also has this strap. So maybe japanese boots have this. *shrugs*
Rinoa complements her dress with some accessories. First of all, she wears armwarmers that has the same material as her dress. It extends from her wrist to just below her elbows. At some points of the game, it is noticeable that there are 2 black stripes that encircles the left armwarmers. But this can only be seen in ingame shots and not in FMVs. These two black stripes acts as placeholders for her weapon, the Blaster Edge.
Also at her left arm, she wears a black ribbon. This is said to signify her rebellion against the Galbadian Army. Though it can also act as a reminder of the Forest Owl's cause of freeing Timber from the Galbadian Army forces. Now, if you have watched Final Fantasy VII: Advent Children, you might have noticed that Tifa's left arm and Cloud's right arm also sport armbands, though this time it's pink rather than black and theirs served as a reminder of the death of Aeris. If you take that into consideration, Rinoa's could also serve as a reminder of the death of several people: first, Julia Heartilly, or second, the Timber people for whose independence she was fighting for.
A most notable accessory she wears is her necklace with a ring dangling from it. Later, we can see that along with her old ring, her necklace also has the Griever ring of Squall which can be clearly seen in the space scene. Looking closer, her necklace's links are comprised of two end circles and a middle oblong one. Also, it's noticable that the Griever's silver has a dull and matted shade which is different from the band of the ring itself. As for her original ring, it's just a plain and simple band. I'm thinking that this ring came from her mother, Julia Heartilly and it might be her wedding band.
The first time we see Rinoa in the game is during the ballroom/graduation scene. The dress she wore here is also the same dress that she wore during the fisherman's horizon concert. Oh, by the way, I'm not a modiste that I'm able to describe her gown in detail.
My PSX renders Rinoa's gown to be yellow somewhat cream. Her dress is mid-thigh length. I don't know the material of it, though. The dress has this one inch bias satin strip at the neckline, wrapping around the dress, crossing at the front and wrapping around her neck. Over the dress is a chiffon layer that extends an inch and a half past the hemline of the dress.
Rinoa's shoes matches the yellow/cream of her dress. It has one and a half inch heels and two straps that wrap around her ankles.
Like her battle dress, Rinoa's wearing some accessories to complement her dress too. First of all she wears a bracelet at her right hand. It's very thin and may only be seen up close. Also she's wearing a necklace. This necklace, unlike the one we see upclose in the space scene, only has her ring on it.