All the behaviors you described up to the point where you said she may have inserted her fingers into her anal cavity are within normal limits. Who brought it to your attention and why is it unclear if she inserted her fingers? Who observed these behaviors and under what circumstances? How was it dealt with when it occurred? Once you know the above, you will be in a better position to know how to proceed. Overall, my suggestion is to tell her that ___ told you they (saw) her doing the described behavior. Tell her that you want to talk to her about it. Assure her that she's not in any trouble and you are not angry with her. Ask her where she learned about it. Ask her if she ever saw anyone doing that or any other "touching" behavior. Ask her if anyone has touched her, asked her to touch them, shown her their private parts or asked her to show hers.. Ask her how she thinks ___ felt when he/she saw her doing the above described behavior. Ask her how she felt when they saw her. This should get the conversation started and her responses to the questions will help guide further questions and any needed actions. The "difficult" part, if you will, is keeping your cool, not showing a strong emotional reaction, holding any conclusions until you have enough information and not lecturing her about what she did or what she needs to do in the future. Try your best to be a good listener. Good luck and let us know how it goes.
I have heard of children having behavior like this -- sometimes it is a soothing type behavior that is a reaction to stress. You should call her pediatrician to see if they have any concerns or comments.