A girl with a good relationship sent a message saying that she loved me.

I should have some feelings for you, but it's more realistic to think about being with my current object, so I said I don't like you.

If you still regard her as your good friend, just pretend that she didn't send you that short message, and don't tell anyone about it, because it may affect her relationship with her current object.

If you love her (note that I mean love), tell her that you love her, too, and don't be shy in front of you.