I think you should go for it - you'll never know unless you don't try, right?
The important thing is not to make a big deal of it. Suggest to her that the two of you spend some time together outside of work and just let her know what a great person you think she is. If she seems glad of the extra attention you're giving her then try to move it on. Don't go over the top with it - just tell her that you think that you would be good together and ask her if she wants to see how things go for a little while. The more casual you make it seem, the less likely it is to make her uncomfortable and damage the friendship if she does happen to say no.
And hey, if she does say no then there are plenty more fish in the sea. If you really value her friendship and she values yours then the fact that you've suggested taking things a bit further really shouldn't ruin that. Just act normally around her and you'll both soon be back to how you were.
Hope you can pluck up the courage! Good luck with it
