Welcome to office life!
Because we spend more time per day in the company of our colleagues than we do with our spouses, close reltionships are absolutely natural, but you have to see them for what they are.
Rest assured, she may well confide in you secrets that she tells no-one else, including her husband - the problem is if you start to interperet this as a deper level of contact than it actually is.
Yes, in some ways, and some areas, you will both have an empathy that she shares with no-one else, but never ever confuse this for something that is lacking in her marriage, and that she would leave her marriage for - it is not.
What you wild have is a deep friendship, which is really good to have, but if you overbalance it by trying to see something that is not there, you will loose her completely.
Accept that she likes and appreciates you, but she has a husband, and it's not you, and won;t be.
It is hard - I have been there, but you must see this clearly, and don;t be distracted by wanting to see things that really aren't there.
There is a very simple golden rule all men whould know about all women. If she wants you to 'move up a notch' in your relationship - she will let you know. If she isn;t letting you know, then she isn;t interested.
It's harsh, but it saves your dignity and her embarassment, always worth it in the end.