Should I ask this girl out online or wait for a chance to run into her again to do it inperson?

She is a friend of my best mates girlfriend, who I used to work with as well. I have seen her and spoken to her maybe half a dozen times while at work "I work in a bar" and she has been very happy and friendly. I saw her new years briefly on my break and I'm kicking myself I didn't ask her out. I wanted to do it in person but at the same time it felt unprofessional and woused out. I added her on Facebook today it's pending but is it worth waiting to see her by chance again to do it in person. Or just send a DM and ask her out at the risk of waiting to long or not seeing her.

Should I ask this girl out online or wait for a chance to run into her again to do it inperson?
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