When puppy doesn't respond to first time command

Hello, I am new here and have a quick question. I do have Ava enrolled into Puppy classes but it's a little too late to call her and I am curious now. Ava is amazingly smart and in my home, she listens to every command including: come, stay, sit, leave it, okay/done, hold, fetch and more. I can tell she just loves to learn. Although, when she gets distracted, it takes a bit more.

If my 10 week old Puppy does not respond to my first command, ie: "Sit", when she usually does, what should I do? I know that you are not supposed to repeat yourself, but I am unsure on what to do than. I do not want her to get away with not listening but I do not want to have to say, "Come. Ava, come. Come. Ava, come.".

Some of the things I have tried:

I have tried letting her see and sniff the treat by putting in by her nose and than raising it above her head to get her to sit. If that doesn't work, I try to push a bit on her bum but that makes me feel like I am going back to first base. If she doesn't want to, she will just get right back up. Stubborn girl =P

If she is out back and I ask her to "Come" she normally will. The odd time, like if she can see the neighbor's Dog, she wont. I rattle the treat cup and if that doesn't work, I pretend to leave her by shutting the door. I have a door where I can stand on my tippy toes and watch her but she can not see me. This doesn't seem to work either! I don't want to run after her so she thinks it's a game so normally, I just wait it out.

What in the world did you do and what worked?