Could really do with some advice regarding an incident today where a child may have broken her finger!

the mindee (almost 3) from a standing position - went to lash out at my daughter (almost 3) - mindee raised her right hand into the air and brought it down towards my daughter but did not make contact - she drew her hand back before she hit her and started crying and holding her hand to her chest.
(this child does quite regularly hit other children and mum is aware of this and I use time out to deal with the issue whilst in my care.)
This happened at about 11.30am - I checked her hand at the time and it looked fine - I just thought it was really strange as she didn't actually make contact with my daughter or anything elst. It looked as though it happened in mid air, but I can only assume that she has cought it on her jumper or sleeve posibly? very odd.

when I looked at her later whilst washing after using the toilet about 13.45 - I could see that her middle finger was really swollen and bruising was appearing. I then contacted mum explained what had happened and said its best that she be taken to the doctor. Mum agreed that she would pick her up or have someone else come to collect her. Mum Didn't get here until just before 5 - missed the bus from town.

I'm now concerned what I should do if the child's finger is broken! I completed an accident form with mum and she has signed it, but i'm worried that there may be some accusation that I wasn't suppervising properly or something along those lines, I was in the room when it happened but there was nothing I could do to prevent it, especially as im not even sure what it was she did!! - Do i need to let OFsted and my Insurance company know if it turns out that the finger is broken? - i'm also concerned she might complain to Ofsted or try and sue me.

Any advice would really be appreciated!