With a child in Y6 and Y1 I can honestly say they even out before the of the school year, yes some Sept babies might learn to read quicker and yes some August might learn to read later but it really does no matter at all, because they will do it when the can and when the are ready. All this worry in based upon not being first at stuff and this is NOT what school is all about. This obsession about top and bottom and somewhere inbetween is frankly pathetic and only causes stress for the child and worry for the teacher. Teachers don't have top and bottom groups, streaming does not happen in primary school!! They help each child as they need it and they see necessary.
Parents of summer born children do not worry at all! Some early born kids in the year are very childlike still and some are very mature, it is certainly not a marker for the whole of their school lives, DS1 is 10 in Y6 and struggled so much with reading till Y2, now in Y6 he's on course for L5 (level 4 being average for end of primary school). Age is not the marker to use as snap judgement!
OP how do you know she's lacking? Do you go into school and watch her? Have you read notes on all the other children? Ignore shit in the papers and listen and talk to your teacher and give you child a chance before you start labelling her as 'less confidant' and 'poo concentration' she's younger, get over it, it won't do her any harm at all, only you will with this sort of negative talk.
Talk to the teacher not read the papers and stop setting your kids up to be failures by sodding constant comparrison, praise her, encourage her and nothing else, you don't know and will never know how other children are doing with their education and social skills you only think you do.