Potty training help!

Hi guys have a question regarding potty training. Currently my 14 week old dachshund has a patch of grass inside of a large pen and her crate is inside the pen. I know that were not supposed to encourage free room at a young age, but Every once in a while, I’ll take her out of the pen to play fetch with her in the apartment and make sure she can run around (she’s not fully vaccinated yet so can’t go outside, I live in NYC in not the cleanest area so it’s hard to get her out).

if she’s in the pen, she’s awesome at peeing specifically on the patch of grass that we got for her. She also always poops in the exact same spot every day on the floor right next to the grass so I’m getting a larger patch of grass so she has places to pee and poop. But if she’s outside the pen, she will never go into pee and will always just pee right on the carpet . Is there a specific way to fix this? Should I be removing the pen? So she can always have easy access to the grass? I always leave the door to the pen open so she could go in there if she wanted to, but I just don’t know what to do and what would be a better way to potty train her.