My puppy does not let me know wher she has to go potty?

I have a 4 month old papillon she is having problems with letting me know she has to go out. I bought a Poochie-Bell and she is scared of it so that's not working. Now I know normally you can tell when they have to go out they sniff around but she does that all of the time so I have a hard time knowing what is just sniffing around for fun and what is I have to go potty sniffing. So I'm wondering what I can do to get her to let me know that she has to go out and also if there is something that is causing her to sniff around all of the time