She sounds very like my daughter, tbh. She's autistic, but her class teacher 18 months ago decided she was spoilt and needed taking down a peg or two (despite all expert reports, and the class teacher from the year before, saying she was a gorgeous child who just needed support with social interaction as she couldn't understand what the rules were) and by the end of the first term she was vomiting from stress. Speech and language therapy to help with social interaction, small group work in her (new, fantastic) school etc helps, but to be honest she can be embarrassing at times. She just doesn't understand that the world isn't her stage because she has no grasp of social context. She's going to need a lot of help and support as she gets older (still primary aged right now) and the balance between making her behaviour adapt appropriately, and not squashing her self esteem yet more, is really hard.
It may not be that at all, but as many pp have said, she's ringing all manner of alarm bells to me. My son's also autistic and presents totally differently - shy, anxious, desperate to please - but my daughter would also think her jokes were the life and soul, when in fact she was disturbing people's quiet enjoyment of a film.
Sadly, if her parents aren't open to investigating this they will not thank you for raising it, unless and until the harm is sufficiently great that she has overt mental health problems, and they're looking for answers... which is usually in early to mid secondary. Primary school teachers very rarely recognise and properly support this sort of autism in boys, let alone girls, so sadly it doesn't seem likely that much will be done. What she really needs is a very competent SLT and OT assessment, and then an ed psych with those reports as backdrop. That would establish if she's got SEN, or just unfortunate traits she will hopefully grow out of.