Any reaction at all (unless you catch her in the act) isn't going to help, she won't understand at all.

There are 2 training ways I'll describe below and then if they don't work, you can try others.

1) Praising. This means you take her outside every 45 minutes. You stay with her outside and wait. Close the door to go inside and wait. When she has done her business (this can take around 5-10 minutes to get close to it) you give her heaps and heaps of praise, and a little treat and lots of attention. Then go inside, if she does something inside and you catch her you say "uh uh" and clean it up without giving her any attention. You can withdrawal attention throughout the day and only give her heaps of praise and attention outside where you want her to do her business. I would leave the mat inside only when you aren't able to do the 45 minute toilet timing.

Her bladder is around the size of a golf ball right now, and it takes around 20-30 minutes to fill up She is only now beginning to get control over the muscle fully, so it shouldn't take too long now!

Training technique #2) Crate training.

You pop her in a crate with some food & water and leave her in there for that 45 minutes, take her outside to the loo and give her all the praise once she does her business. Then play with her and cuddle her and pop her back in the crate for 45 minutes with something to chew on. You only need to do this for 1-2 full days to see improvement.

most of all remember she won't want to go outside without someone with her, its cold there too and if something distracts her from inside, she may stop halfway... and toddle inside to see whats going on and then bust the rest out when she gets excited.... so its important that whatever technique you use, you make sure going to the toilet is the most exciting thing for a few days.