So I recently came across a girl I haven't seen in a while (were friends) and found out she is now single. What would be the best way of showing I'm not JUST a friend?

For now just comfort her. When the time is right, jump on it. Just make sure you don't get put in the friend zone.

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I recall reading an article about your situation. I remember it recommend something like:

First make sure you know your goal. Give her some time to heal and let her know your there for her. But most importantly, LET HER KNOW your interested in her. Straight up tell her. 'I know your going through a rough time with the break up and I want you to know I'm here for you but I also need you to know I want to be more than just friends. I can wait till your heal but I just needed you to know.'

This way, after she's all heal up and you go make a move, she won't be like let's just be friends. If she's really not interested, then hopefully she'll let you know so you know your just a friend and in the end you'll just be friends. In that case look for someone else but still be man and help her through the rough time. If she doesn't say anything and let you help her then she may give you a chance once she's heal up. You get my point.

Any PUA opinion?

Personally I wouldn't just root myself in the friend zone, if you try to give her time to recover then before you know it she'll just be asking you advice about the next person she's dating and you'll be kicking yourself.

I also wouldn't advertise my interests directly and up front, as that kills the magic and makes you instantly into a boring easy catch.

My opinion is start from the friendzone but start working yourself out now.
comfort her, hang out with her, make her laugh, make jokes, make physical contact, make joking negs, etc. Make suggestions about how you might be interested in dating her without saying it outright to get her thinking about it, perhaps escalate and then pull back and say, "no, we shouldn't..." etc.