When girls kiss other girls (lips or cheeks) could it be a way of showing social status?
That's a good question, but it doesn't have a definitive answer. ANYTHING can be a sign of social status if the people in that environment accept it as such. For example, just having an expensive phone could be a measure of social status because only a wealthy person could afford such a thing.
The argument against it would be that men and women have been kissing each-other on the cheeks as a greeting throughout history and it doesn't has to be related to social status. The problem with this is that just because kissing is used as a greeting in many places (though thankfully NOT in the U.S.) that doesn't preclude it from being used as a status symbol.
The argument for it would be if the kissing on the cheek were done selectively...then, it could be said that receiving such a kiss would be a sign of having been chosen by someone else (and therefore accepted as worthy.) The problem with this interpretation is that true status symbols are generally rare or guarded (such as a secret handshake.) A kiss is free and therefore people of lower social status could mimic it easily with each-other, thus diluting its effect. In addition, it would only have the effect of demonstrating status if the person who chose to do the kissing had status themselves; being kissed by a "loser," for example, would therefore have the effect of associating you with them and therefore would actually lower your status.
Basically, my instinct says the answer to your question is NO. It is too common a practice, too easy, and has too many meanings across the world to be used consistently in that way. But hey, who knows? If cool tattoos can give a person status, why not a kiss?
I do not think that girls kissing each other is meant as a way of showing social status.
Females who kiss each other on the lips (if straight) are typically doing so to get attention. We see this most commonly in celebrities who do such things at awards ceremonies or other public performances. I would argue that this is mostly a way to create "buzz."
As far as kissing on the cheeks, I really think that this is just a way of showing affection that is not really any different from a hug. Certainly, it communicates social status in the sense that it communicates the idea that the two are in the same social circle and are friends. However, I do not think that it is meant to in any way tell us about the relative social statuses of the two women/girls.