This happens to everyone at some point. Little kids explore every orafice on their bodies at some point; it's normal. To complicate matters (for parents!) kids feel pleasure touching their private areas and we are uncomfortable with that plus it isn't socially acceptable. So for their own safety and to teach appropriate social behaviors, it's important to set some boundaries for our little ones.
In our house we talk about public versus private discussions, behaviors, and body parts. As a "big" girl its important to go ahead and start learning those boundaries in non-scary ways. If you don't teach her, she will either do something really embaressing or she may be confronted with a situation where another child does something inappropriate and she doesn't know better, or worse.
I have told my oldest that she has private areas where her pee and poop come from (and she also knows that she has a vagina where babies will someday come from-- we watched Discovery Health baby shows when I was pregnant with her sister). She knows that there are public areas of the body, like arms and legs-- anywhere not covered by a bathing suit. Public areas are ok to show to people outside of our household and are ok to touch and be touched on (ie a friedn can touch your arm or hodl your hand). But, private areas are different. We have told her that it is not polite to show others our private areas or to touch our private areas in front of other people. To help protect her, we have also told her that it is not polite to look at or touch other people's private areas or for them to try to see or touch hers, and that if anyone (other kids or otherwise) tries to do inappropriate things concerning private areas, then that is something that she needs to talk to mom and/or dad about.
To keep the conversation from being too sexually oriented and causing her to fixate on that, we also talk about other public versus private things. For example, we've told her that, for our family, talking about how much money we have (or don't have) is a private issue that we keep within our family. What you deem public or private is specific for your family and might be something that you might want to begin discussing with her as well. We talk about public and private issues periodically and I ask my daughter about hypothetical situations to see if she thinks they are public or private. For example, I might ask, "Say Becca tells you that she is wearing cool new Dora the Explorer panties, and asks if you want to see them. Is that something that should be public or private?" When she answers "private." I then ask her what she should say to Becca, and and encourage her to let me know if situations like that occur. Obviously that situation wouldn't be a big deal, but I want for my girl to know that she should tell me when she feels something that should be private happens in the wrong context. I also give her hypothetical situations about other private issues like money or a duscussion between mom and dad, or whatever...
Regarding putting toys into herself, that is an issue that I believe should be addressed, though you should be careful not to assign it more meaning than it really has. At her age kids do touch themsleves and find it to be pleasurable, but are they really masturbating, I personally don't believe so. Just like little kids put things up in their nose, and we have to teach them not to, they will put things into any and every orafice that they have, and for their own saftey we do need to teach what it isn't appropriate. Our pediatrician cautions that you don't want kids sticking toys into their genitals or anuses as, in extreme cases, things can get stuck or abbrade their flesh, or they may spread germs from anus to vagina (and cause a UTI), or from anus (or vagina) to mouth (and cause something really bad like E. coli). Bacteria (like E.coli) that normally reside in the anus (or genitals) can be dangerous to the health when moved to other points in the body, but little kids aren't really mature enough to be cogniscent of that. So, in our house, the rule is that we don't stick things into our private areas because we don't want to accidentally get hurt or get an infection. My daughter once stuck tangerine seeds up all the way into the bony part of her nose and got them lodged in there. So, I remind her of that situation and explain that we don't want to get anything stuck in any opening of our bdy because it isn't good and it can hurt (which she remembers quite well from the nose incident).