Hugging is one of those things that's worth doing right. I really hate the tepid one-armed bump-and-pat that some people do--it makes me feel like they can barely stand to touch me, and if that's the case, I wish they wouldn't bother. It's worse than the limp handshake.

I don't think there's such a thing as a 'professional hug', because I feel like in general you wouldn't be hugging someone at work unless you already had a more personal relationship with them. For example, I wouldn't hug my boss's boss at all, because I barely know her despite our professional interactions, but when I hug my boss, I hug her like I'd hug you (well, maybe a tiny bit less enthusiastically, but it's a real hug nonetheless), because we're more than just boss and employee to each other. We've been out drinking.

It sounds like you did exactly the right thing with your freelancer, because your interaction with her already included personal things.

Short answer--if you've got the kind of relationship where you can hug someone, give it your all.

You know who else gives amazing hugs? couplingchaos. She hugs like she means it, and I appreciate that.