What would you do if you saw your ATF randomly walking on the streets?
would you go up to them?  
IMO If i was real close with them and seen them on a regular basis then yes i would go up to them

This has been discussed many times. The only exception is if you are both alone and she gives you a clear signal she'd welcome a hello. Otherwise, walk on.

How long have we known each other? What is her personality like? Is she "out?" Is she single? What are the surroundings?If in doubt at all though, let it be. It could open a major can of worms for her.

Many of our hostesses are "regular people" with real jobs, families, local friends. You, the OP, might not have any problem being "outed" in public but many of us clients also have real jobs, families, local friends, etc..  
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If you were out someplace and family or business associates or friends were nearby, would you want an apparent stranger to come up to and say, "Viper! How are you? Long time no see." or ANYTHING that puts you on the spot with others?  "Hay, Ralph, why did she call you Viper?"  
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I think that most of us follow the rule to say nothing and do nothing or almost nothing. I think if there is mutual eye contact with someone you know that it is very hard not to nod your head a bit or to briefly curl your mouth into a small smile.
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If you have a prior agreement with someone -- "No problem! Just come over and say hello!" "Same for me!" -- I would even tread there carefully. It could be a rare occasion where her mother or sister (or husband) is with her in public and she does NOT want an open, effusive greeting. Take it slow and let her initial reaction ("I'm sorry, you must have me confused with someone else." vs "Great to see you, too!") guide you.