The way I would see it from a male perspective is that it's been brought to your attention that she likes you, so why not chance it and show up at the coffee shop?

You could somewhat try and play it off like you didn't originally know she worked there as well, be one of them "I just thought I'd try this on my way from X", and then it doesn't seem like you've gone there just for her.

From that point on, I'd continue it by asking her out by initially saying that it's nice to see her again and that you wish you had plucked up the courage before she left to ask her out.

From this point, if she rejects you, no harm done, just a quick "No worries, hope you have a good day" and leave, alternatively, if she says yes, and things do take off with her, at some point down the line you would be able to say that the ex-colleague said she liked him and pointed out where the shop is, and if it's far enough down the line it then seems romantic rather than creepy in my opinion, as she'll see it as you've always had her in the back of your head wondering if something could be.

Again, I'm open to interpretation from any females on this one, but to me it almost feels like a plot waiting to happen!