Hi op, I read your thread last night but didn't have time to reply. I am glad the school are taking your daughters complaint seriously, this type of incident in my experience is always upsetting/ shocking and as a result dealt with swiftly and firmly. It is so important for this kind of incident to be approached at a whole school level, this would be a great opportunity for discussions of the nspcc underwear rule for example. One school I taught at, there was an escalation of this situation, I will just say that there was more than just looking involved (older children 11/12) and this was a very distressing incident for everyone involved.
Often children who show overtly sexualized behaviour, have been the victim of abuse themselves and have a skewed perception of appropriate boundaries. So these situations require a great deal of sensitivity and understanding.
Slightly off topic, but I have recently read an article, which claimed children as young as seven are being exposed to pornography! Mostly due to a lack of supervision during use of electronic devices. There are seven year olds who are bought iPhone 5/6/7's/ iPads for Christmas, which they can then take outside when playing with friends. If children are viewing pornography then I can only see an increase in incidents like this happening. When the young mind is struggling to process situations that are beyond their comprehension, they resort to the method of learning that has carried them from babyhood onwards - play (roleplay). I want to stress that I am in no way suggesting that this is the case in the OP's situation. Nor am I using it as an excuse for this behaviour. I am just despairing at a world that leaves young children, open to exposure to materials that would shock many adults. The NSPCC has some fantastic information on protecting children from the darker side of the internet.
This link is fantastic for preventing children from being exposed to inappropriate content online (Perhaps not so relevant for you OP but hopefully someone reading will find it herlpful!)
www.nspcc.org.uk/preventing-abuse/keeping-children-safe/online-safety/parental-controls/
This following link lists the different types of abuse, there is a section on bullying and also harmful sexual behaviour - You could contact the nspcc helpline on 0808 800 5000 .They may be able to advise you on how to help your daughter to cope with her feelings surrounding both incidents. Alternatively they do have a plethora of information on their website.
www.nspcc.org.uk/preventing-abuse/child-abuse-and-neglect/
These following links are meant for teachers but there are leaflets to download and the planning information might help with how to approach the subjects with children.
www.nspcc.org.uk/preventing-abuse/keeping-children-safe/underwear-rule/underwear-rule-schools-teaching-resources/
www.nspcc.org.uk/preventing-abuse/keeping-children-safe/share-aware/teaching-resources/
I have also linked several books which might help your daughter, perhaps your local library will have them?
www.amazon.co.uk/Your-Body-Belongs-Cornelia-Spelman/dp/0807594733/ref=pd_sim_14_2?_encoding=UTF8&psc=1&refRID=FHKDK7ZK88HV00C2GP6H
www.amazon.co.uk/Said-Guide-Keeping-Private-Parts/dp/1878076493/ref=pd_bxgy_14_img_2?_encoding=UTF8&psc=1&refRID=QGHKVGZW2CMYPRMP2HEV
www.amazon.co.uk/d/Books/No-Means-Jayneen-Sanders/1925089223/ref=pd_cp_14_4?_encoding=UTF8&psc=1&refRID=6DW119TSTMAENDC1A7CY
www.amazon.co.uk/d/Books/My-Underpants-Rule-Rod-Power/0992953006/ref=pd_cp_14_2?_encoding=UTF8&psc=1&refRID=5HA9ZK8AS5AW282G8B3K
I'm sorry your little girl has been treated this way, your daughter was very brave to tell you about these incidents and it shows the loving relationship you have with your daughter, that she felt able to confide in you! Hopefully now the school are dealing with this incident your daughter will feel safe again.