I'm not quite sure how old Kaylee is as I post this, but it is not uncommon for most pups to regress a little. Just when we think we have a routine down pat, they change, or go through a life change, such as teething, or just growing up.
You mentioned that you are taking her out once an hour, and that she can hold it for up to 4 hours when you are at work. She knows when you are not home, so I would suggest that you go back to taking her out every 20 minutes, not once an hour. Remember to praise, praise, praise the successes and ignore the failures. Remember, they are yours, not hers!
Lana's Mum brought up an excellent point about always using the same door to exit when it's time for business. Slowly you will notice that the pup will head to "the door" and you must be paying attention at all times. The first few times, which are critical, must be successful. Literally drop whatever it is you are doing and rush that pup outside. They have about 60 seconds before they can't hold it once the thought occurs.
You'll know when you've really made a mistake when you find the business right in front of the door to the outside. That means whomever was "on duty" didn't pay enough attention.
Lastly, always be mindful that there is not an underlying health issue. If it's a mild set back as in Kaylee's case, and you change things like going out every 20 minutes and still have accidents, or notice other uncommon behaviours, it might be time for a visit to the Vet. Try the changes first for several days.
Don't give up hope! Even after they are considered trained, they will still have the odd accident for whatever reason (especially males in my opinion). No puppy is 100% trained until they are 1 year old. It just starts to become more predictable around six months of age, once the majority of teething is over.
Good luck and hang in there. Consistency is key, and so is praise for a job well done.