stands + related info
I figured it'd be a good idea to lay this out, so there isn't any sort of confusion and it's easier for other players to figure out how characters would/wouldn't react to Jolyne's stand + stand ability. JoJo-verse reasoning gets a little hazy when other, vastly different, realities come into play, so bear with me.
First off, not everyone can see stands.
Traditionally, only other stand users can see/sense them, but that's not really very helpful where multifandom games are concerned, SO. My logic here is based on the entirety of JoJo-verse, so hopefully it'll make sense.
1. Normal, average, everyday people can't see stands. They can see things caused by stands, like holes punched in the wall, but it would be more like "HOLY SHIT WHAT JUST HAPPENED WHY IS THERE SUDDENLY A HOLE IN THE WALL?!" This goes for stand-related abilities, like Jolyne unraveling into string, too. Although in that case, it's more of a "...where is this string coming from?" sort of situation, because they likely would be able to see the string, but wouldn't be able to tell that it originates from Jolyne. Also, to normal people, if Jolyne has unraveled say... an entire arm, it'll look like she's suddenly lost an arm. Freaky. I'm... uh, not quite sure what it would look like if she twisted her chest into the infinity symbol (WHICH HAPPENS IN CANON), but uh. I doubt she'd be on the Plane while that was happening so we'll cross that bridge when we get to it.
2. People with unusual abilities can see stands. Obviously, other stand users can see stands, but that's pretty much only relevant to JoJo-verse. Basically, if a character has some sort of magical/otherworldly/nonhuman ability, they'll be able to see stands. I think that's pretty self-explanitory?
3. Animals can see stands. So can sentient plants. Oh, and so can plants that used to be animals or are plant/animal hybrids. Seriously, I cannot make this shit up. JoJo-verse is weird. Any of the above can also have stands, too, but that's kinda irrelevant.
4. Extraterrestrials, Vampires and Things Which Aren't From Earth can see stands. There's an alien in Part 4 that seems able to see stands, and a vampire in Parts 1 and 3 who winds up having a stand, so why not.
Random stand-related info
Stands are a lot like personas in the MegaTen/Persona/Digital Devil Saga series: they're a manifestation of the stand user's soul, but are still connected to the user. Damage done to one will affect the other and vice versa. Stands tend to look drastically different than their user, hence why figuring out a stand's user is often frustratingly difficult. Stands aren't kept out at all times, and generally will only appear at the behest of the user. Some stands have no real form at all, but since that doesn't apply to Jolyne's, I'll skip over it.
Up until part 5 of JoJo canon, stand abilities weren't carried over to their users. Meaning, the stands could do super special awesome weird shit, but the user himself couldn't. Part 5 had a few characters able to utilize their stand's abilities on their own, but in part 6, which would be Jolyne's arc, oftentimes stand users have the same abilities as their stands.
For Jolyne, this means she can literally unravel any part of her body into strings, and can manipulate the thickness and durability of said strings. Her stand, Stone Free, can do the same thing - but can also punch really hard and really fast from strengthening the strings at a given point or something idk.
Obviously when the strings are broken, it causes Jolyne injury. The more strings break, the more blood she'll have gushing from random parts of her body. Also, manipulating strings near the heart is a (very) bad idea, as there's a good likelihood of straining her body/damaging her heart/killing her.
Something else to note is that as of Part 6, anyone can become a stand user. The easiest/most common way is by inserting a 'stand disc' into your head. The discs are actually an ability of the stand White Snake - in Jolyne's canon, these discs can store a person's memories or stand ability. Put a 'memory disc' into your head and you'll be able to watch the memories of the original owner. Put a 'stand disc' into your head and you'll be able to call on and use the stand contained therein. There ARE some exceptions - basically, if the stand is very powerful (like her dad's Star Platinum), there's a high probability it will reject anyone other than its original user. But considering that there aren't many super powerful stands, it's not much of an issue here. ANYWAY.
Inserting a 'stand disc' into someone who is already a stand user will enable them to use both their own stand, and the addition stand in the stand disc but generally having more than one stand is a bad idea and will negatively affect the user. If a person's 'memories' and 'stand' are removed as discs, it will leave them in a comatose state which will eventually lead to death if the discs aren't returned. The only one able to remove memories and stands in disc form is White Snake. If someone is knocked unconscious and have used/been implanted with a disc, the disc will pop out/appear. It's kinda like having a CD ROM drive in your head.
If I think of more ramblings, I'll add to this.