
It isn't going to be easy as she has had 4 yrs of a very set life,you need to take it slowly and be patient. Is there some way of you taking her crate to work with you as it will have her scent on it already,if not then a pad she has wee'd on to put in a crate at work, when she does use it give her a high value treat,strong cheddar works here,they don't need much to get the taste.
She may have been dehydrated and under fed which will explain why she didn't toilet for so long, was she very thirsty or hungry on arrival?
Dealing with a new home and new surroundings at work is probably overwhelming for her to cope with, normally if it was a pup you would work on one place at a time.
I would continue the trips to the garden so she gets used to the sounds and smells and relaxes enough to toilet out there.don't set her up to soil elsewhere in the house by removing the crate and pad, the weather should improve soon so she can have free access to the garden with the door left open.
Good on you taking on this challenge