I'm a bit late to this so OP I've read your posts but not everyone else's.
From what I gather dd has either taken a 30credit module or 2 x 15 credit modules with a group and scored 43 which has dragged her overall score down and this was in year 2?
Unfortunately the time to appeal this grade was when she took it last year.
I've been to 5 different uni (long story involving changes in career and other things not relevant).
The way things often work is you hand in a piece of work and it is graded, you get that mark but it is provisional. At the end of the year (sometimes the semester) the grades go through a verification process. This will involve a committee at the uni and there will also be someone from a different uni.
This is where grades are finalised and where any mitigating circumstances are taken in to account. At this point the grades are either finalised (can go up or down but rarely do) or the student is given an opportunity to resubmit some work, sometimes you are given an option, eg one module I'd scored A16 (grades were A16 A15 etc down to D5) on an exam but due to illness the written work had not been handed in, in normal circumstances this would mean a max score of D5 but I was given mitigation so my work could be submitted late 'without penalty'.
OK sorry for the ramble, but once a grade has gone through this process it is final.
So dd should have known going in to year 3 that she had 30 credits ie 2 modules at 43% so had to up her game for the final year.
I'm sorry, I know it is unfair when members of the group are like that. I had to do a few group modules, in one we started with 4 in the group, we could never meet as a 4 due to commitments, 1 person left the uni part way through, another contributed zero, hated that we had written a presentation without her and she didn't like it so complained to the head of department, despite the fact we had got a good grade, she then refused to work with the two of us remaining, so we ended up completing it as 2 people.
I tell you (and your daughter) this just to show I've been there and it is unfair.
There is usually a section you have to sign when you hand in to say this is your work, and often you have to give an account of how the group worked, what they did etc -if dd had this, that is when she should have outlined the difficulties.
As for the student posting on social media, saying he is glad, please screen print this and send it to the uni. It will not change dd's grade but it may cause him problems with the uni.
If he is a non EU student also send the screen shot to the boarder agency, he is in breach of his visa regulations.
Oops just had a quick skim - if this unit is in the final year she may be able to apply for retrospective mitigation using the message as evidence that he deliberately failed.
Non EU students need a CAS from the uni, if a student has failed and needs to extend their visa then the uni " is obliged to consider whether attendance and academic progress is satisfactory and assess the student's continued ability to pass the course"
And congratulations to dd oon getting a degree and a good degree at that. I know it feels like everyone and their dog has a degree these days, they don't.