Under the 2001 Code of Practice, every child that was on the SEN Register had to have an IEP, and the document was provided by the CoP.
since the Children and Families Bill of 2014, there has been no 'set document'.
Some schools devised their own
Some LAs worked together on devising various support plans
Some schools decided to keep calling it an IEP.
Whichever the school has done, it still needs to record the differentiation it is putting in place, and how your dd makes progress with the additional support / differentiation she is getting.
It might be that the Infant school did have one, and just never invited you to a meeting - in which case the Junior school will review how she has got on with those targets, and decided if:
a) she has made so much progress she no longer needs a Plan
or
b) she has done well, and achieved those targets, but still need support - in which case you will set new targets together
or
c) She has not made very much progress, despite being given additional support, and (together) you will need to look at what additional support could go in for her.
If, for some reason she hasn't had one previously, then the Junior school will write one for her, with your support.
Ideally, there will be you, the SENCo and the class teacher or maybe a LSA if she has one (?) in the meeting. In reality, it is more than likely to be just you and the SENCO. She will sort all the paperwork. (you should get a copy once it is written up).
The new CoP is also very keen to 'hear the child's voice' so some schools invite them in to the meeting, others talk to them beforehand as feel a meeting can be a bit overwhelming.
She (together with you) will set targets that you both believe your dd can achieve in 3 months time, and it will set out what they will be putting in place to help her achieve that.