Too young to be on Instagram, even if all her friends are. Remove that, and your problem is solved.
The age recommendations are 13+, and as said there for a reason.
She is too young to fully understand the risks involved, and even if the account is fully supervised you will be unable to stop her searching a pleasant variety of #hashtags using words that mean one thing to an adult, and competely another to a child. R-rated content abounds amongst seemingly innocuous word combinations.
Does she understand even with a private account ( which I hope you have insisted on), who she should accept as friends? Does she use a passport style photo and her real name? Do you regularly review her friends list? Do you understand what the necessary settings are? Do you understand the emoji language, used frequently to get around parents who supervise accounts? ? Does she know how to report , block and ban? Does she understand what a digital footprint means? Did you know she can be bullied by the disappearing DM feature?That you might not actually be reading all the texts? Does she know what's appropriate to take photos of and what is not? Tha's alot for me to type- and it's the remarkable 9 year old that can understand all that.
Instagram was ranked the the worst app for causing mental health issues in pre-teeens and teen girls last year. More and more studies are rolling out showing how detrimental it is for developing teens, let alone children. It creates low self-esteem, FOMO in teens, and teaches then a horrible message about linking your self-worth to the number of likes and your appearance. Kids will do really stupid things to get the validation from peers that they want.
And for the poster who stated banning is ineffectual, that is advice and reasons given more often for parents using it as a means to punish kids for mis-using social media at an older age than 9. A punishment. Not as a preventative measure.
If as a parent, you secure the app store, and install a supervisory app that details a childs activity on your server at that age, you can stop them pretty thoroughly from having any social media. Qustodio or Net Nammy are good options.
Nine is too young for social media, I cannot emphasize this enough.