Visual: Emma is considered notably good looking in-universe, to the point one of her monikers is "mysterious beauty". She has a very noticeable amount of muscle around her hips and thighs, but as shown in animator artwork her arms are quite toned as well. For reasons best known to weird Yu-Gi-Oh design choices, she also has pointed ears, and the way she wears her hair makes them pretty obvious. She's shown wearing lipstick literally all the time, even when she's at home (though that could just be a case of not bothering to take it off).
Fashion: Emma's usual outfit is the motorcycling outfit pictured to the left, however, if she's just at home coding or something, she tends to wear a short-sleeved hoodie and matching shorts. In general, if she's out she tends to walk the line between practical and showing herself off, and when she's at home she's a bit lazier with her clothing.
Her current VR outfit is a short-sleeved one-piece with a high collar, worn with fingerless gloves, diagonally cut stockings and boots with a heavy tread on the soles. If she ever has to make a "work outfit" outside of Link VRAINS, chances are it'll be along those same lines.
Demeanour: Emma has a very confident, self-assured kind of air, and tends to come off like she knows what she's doing at all times unless she's in a very bad situation. Her manner is fairly casual and often borderlines flirtatious, though it's typically not genuine so much as her trying to ease people's suspicions for her own purposes. In her work, she's professional but playful, in the sense of someone who's very good at their job and enjoys doing it, and has the kind of curious air that would be expected of someone who's a self-described "cyber treasure hunter". In private she tends to be more casual and almost lazy.
Sound: Emma has a fairly high voice and a playful tone (example here), though has a distinctively older speaking style, as she observes at one point when she's caught out impersonating a teenager and describes herself as speaking "like an old woman". She tends to amp this up if she's intentionally flattering someone to get in under their guard. On the reverse of that, if she's on a mission or discussing something more serious, she tends to tone it down and take a more mature, straightforward manner of speaking.

VRAINS is set in the futuristic metropolis of Den City, where the major tech company SOL Technologies has created a massive virtual reality that's become a hit with the population. This VR, known as Link VRAINS, creates a space for Duelists to battle with all the effects and realistic monsters they could ever want, as well as letting people market their skills or selves with virtual avatars rather than having to attach their real life identities to any of it.
Emma is a well-regarded hacker for hire within this virtual world, going by Ghost Girl, and will take any number of risky or questionable jobs if the price is right. Perhaps courtesy of her ability to hack the SOL Tech database if she wants to, she's in regular contact with at least one of their members and has an established business relationship with them and other companies who want to avoid being on the wrong end of her hacking skills. It's through this she ends up dragged into the plot, when Akira Zaizen of SOL Tech hires her to capture the VR vigilante Playmaker and his near-human AI companion, and her superior hacking skills to the vast majority of VRAINS' cast comes in handy quite often over the course of the story.

As previously mentioned, Emma is an incredibly skilled hacker even within the context of VRAINS, where a huge chunk of the cast are skilled hackers. Her first appearance involves her coding a complicated trap into VRAINS (i.e. she had to hack into SOL Tech and VRAINS itself before she could even start coding the trap part) overnight while mostly running on coffee, and typically the only instances of her coding skills failing involve her running into things like the Ignis that use programs she and most of the world are entirely unfamiliar with. She's routinely turned to by even major companies that employ massive numbers of experienced coders, and when pitted against other, more "bounty hunter" type VRAINS hackers, outsmarts and outcodes them extremely easily.
As navigating Link VRAINS is often akin to navigating real environments, Emma is about as fit and toned as you would expect someone who raids hostile environments for a living would be. She also occasionally demonstrates skill with more RL sneaky abilities like lockpicking and sleight of hand, and definitely leans towards the social engineering style of hacking in some cases with more deceptive, manipulative methods. She is apparently considered a very good duelist in-universe, despite VRAINS' plot not lending itself to minor characters winning major duels basically ever.