@elwynn,
Are you taking her outside for any reason other than for a bathroom break?
And by house trained, do you mean she only 'goes' when outside, as a matter of timing, or has she developed a signal yet for you to recognize she needs out?
If she doesn't let you know she needs out, she isn't house trained.
Dogs are smart. Is 'outside' a reward or punishment? She might be distracted outside, playing and exploring, as puppies tend to do.
Also, puppy’s bodies and metabolism change. She might need to go out more often than before. I've had puppies I had to let out every couple of hours as their diet developed over time.