Girls, How can I confess feelings to my online friend?

I have a friend I have been talking to online. We haven't been in contact for a long time but I can't deny the fact that I already like her a lot and I really want to be more than just friends with her. She told me today that she is meeting up with a longtime online friend in a few days. I don't know if her friend is male or female or whether it's purely platonic or nor but, it gave me a sense of urgency. So my question is twofold. When do I confess my feelings? How do I do it in the best way possible?
Girls, How can I confess feelings to my online friend?
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