A crush is a self-created fantasy.
The truth is that if you actually got involved with her, somewhere between 1 date and 3 years you stand a 50/50 chance of HATING her.
You let go of a crush the same way you let go of any other kind of addiction.
You refuse to engage in that addiction, you tolerate the withdrawal symptoms, and by refusing to dwell on the addiction and instead keeping yourself otherwise occupied, it slowly dies out.
It can take 4-8 months, so be patient. And if you have not totally gotten over your addiction within a year, get some therapy.
In the case of being addicted to a person OR to a fantasy-crush, you need to avoid that person as much as possible. Drop them off of your FB and all other social media. Don't talk with them, except when you must discuss work tasks. Don't LOOK at them. Stop having her drive you home.
Since you work with her, UNLESS you want to create an enemy at work .. confess that you have a crush on her and are now going to let it die out. To please not get offended if you stop socializing or hanging out with her, because that is the only way you are going to get over your crush.