Your feelings are your feelings, they just are. The best thing to do with them is to let them flow naturally. Asking whether someone else thinks it is wrong for you to feel this way, that, in my opinion, is wrong. There is no "you should feel this not that". That is like telling rain it should not be.

A more productive question may be why do you feel this way? And that question, it seems to me, you got. You mourn her young life. In a way she is you, having in a way "replaced you", so maybe you also mourn yourself, your loss, and maybe your own mortality.

The intensity of your expression may have something to do with some unexpressed grief, unmourned loss you carry. A person may find themselves weeping over a kitty (unknown, not their own pet) struck by a car, sad little lifeless body crumpled by the curb. May have walked by such a scene many times without so much as brief "oh!", but now is overwhelmed by an ocean of grief. Who knows why.

I believe it is also very natural to experience "I could have befriended her" thoughts, that is part of grief. Here is a girl you didn't get to know, and now you never will. What a loss! On that note, here is a piece of poem for you: