I'm an English teacher & examiner (GCSE, IB, various boards, 20 years at the chalkface etc etc) & I'd agree with LolaSmiles on pretty much everything here.
I analyse the subject results for my school, & advise on reviews. We do it by grade boundary.
Student with a disappointing result & considerably closer to the higher than lower boundary? Worth a punt! We're private, & parents routinely pay anyway, but obviously we tell them if we think it's worth their while or not.
Student significantly closer to lower boundary? We will advise against, in case the result goes down, but if the parent or student absolutely insists we give them the caveats, they pay, & it's on them if it goes badly wrong.
Honestly, shifts which affect a final grade are vanishingly rare.
I've processed 20 odd appeals in my subject this year over both GCSE & IB & had one upheld - & that was a 4000 word extended essay for IB, not an exam paper. I examine extended essays myself & they are tricksy little buggers & subjective AF. Exams, not so much.
The scanning issue shouldn't be a problem. The software prompts you, as an examiner, to flag up ANYTHING untoward in terms of missing bits of answers ie wrong question wrong booklet.
Although 9/10 times it's missing additional sheets. Top tip: learn to write within the answer booklet provided, because some examiners won't be arsed to flag up an answer that carries on to additional sheets if those have somehow fallen down the back of the scanner, & they quite often do - if you do use additional pages indicate very clearly 'cont next booklet', so it's not assumed you just ran out of time.
Also, OP, sorry, but yes, you absolutely need to pay up & no, often teachers won't be in on Results Day.
This year I was furiously arguing with my Head of 6th Form that he (on the spot on the day) should authorise a review for a girl in my IB class who had uncharacteristically tanked a key paper. I was having this argument whilst squinting at a spreadsheet on my phone from a tent on a different continent.
As it turned out, she had just absolutely mucked it up, bless her.
But no, teachers aren't required to be on site in results' day. It's our unpaid holiday.
Sorry your dd didn't get the result she hoped for, though 