If you're going to bell train, leave them by the door. Hit them with her paw on the way out the door every time. Your goal is for her to ring those when she's out of her expen, out about in the house, to tell you.
As for the other parts of what Dave and Tom said, they are truly the experts in this department. Listen to every ounce of what they tell you. As far as what I learned from my experience with Trooper is that I gave him too much space too soon, and he took a bug backslide at around 14 weeks. It was kind of a nightmare, but after I figured out where I went wrong, I corrected it and he got back on track. Don't make the expen huge (I think you fixed that up already, huh?) and don't let your pup have access to a hugggggge space when out and about. Certainly keep her under your constant watch, but don't allow her to have roam of the whole main floor of your house while out. It'll make it easier for you to watch, catch, and haul butt outside. Then, only after she is 100% reliable on the pad in the expen for a goooood while, SLOWLY make the expen bigger. And when she's 100% reliable in one room (meaning you catch her signals and take her out so there are no accidents) then SLOWLY allow more room to roam when out and about. THIS is the advice I learned from digging up old threads here when I had a freak out "what is going wrong here" "he'll never get it" moment. It was all me. After he was starting to get it I gave too much space too soon AND expected him to get to his pad. Wrong and wrong. Luckily I figured it out real quick before his accidents became habits.
And on top of it, they go thru growth spurts around 13 weeks, and it seems like they go out super often for a little bit of tinkle each time for a little while. During this time they seem to forget all the know about potty training, so be forewarned that it may seem like she backslides in a few weeks.
BUT then one day it just will click for her and you'll realize it's been a week without an accident, then longer. I can't even explain it. I swear Trooper just got it one say and we haven't had an accident since. Wish I could remember how long it's been.
Ps, every hour is not nearly enough. For Trooper it was every 15 minutes of out and about time. I'd set a timer for 13 minutes and take him. Not even kidding.
Hang in there!!! It'll happen!!! Promise!