It seems odd that your DD would have a flat level of 2c (13pts) then an exact rise of 2 points per subject (up to 15pts - 2b) across the board 
That said, the NC has levels. Level 1, 2, 3, 4, etc. They are the only official levels. Sub-levels aren't really 'there' - schools use them to monitor the 'baby-steps' between levels.
2c is 13 pts on the NC scale. 2b is 15 points - the end of KS1 'expected' level.
Then, over the next 4 years, the child is expected to gain 2 levels, or 12 points, to reach a '4b'.
'Expected progress' is 3 points per year on average.
If you drew a chart using The primary tool kit for your DD, the results are:
Writing -by Year 3 summer, she was 1 pt below her expected score. By Year 4 summer, she was 3 points below her 'expected' score (1 year's worth of progress, in other words). However, now, in Year 5, she's currently only 1 point below her expected score again. So to meet her expected 'end of KS2' target (which should be a 4c because it's 2 levels/12 points above her end of KS1 score), she'll have to make 6 points progress over the next 5 terms, which is the equivalent of a child without difficulty making expected progress plus 1/5 (20%).
English - by Year 3 summer, she was 1 pt below her expected score. By Year 4 summer, she was 2pts below her expected score (2/3 of a year's progress). Now, in Year 5, she's still 2 pts below her expected score, so to meet her end of KS2 target, she'll have to make 7 points progress over the next 5 terms, which is the equivalent of a child without difficulty making expected progress plus 2/5 (40%)
Maths - by Year 3 summer, she was 1 pt below her expected score. By Year 4 summer, she was 3 pts below her expected score (1 year's worth of progress). However, now in Year 5, she's still 3 points below her expected score, so to meet her end of KS2 target, she'll have to make 8 pts progress over the next 5 terms, so the same as a child with no difficulty making expected progress plus 3/5 (60%).
I think my argument would be that unless they think your DD is so amazing that the current provision for her will allow her to achieve between 20-60% better than her NT peers, then she will not meet the expectations set by her end of KS1 scores, even taking into account the lower starting position.