First ... Elayne resorted to a method she knew the nobility of her land would accept. It's clear from the reaction that everyone involved with her decision to let the Borderlanders through on the authority of an AS that this was a legitimate authority. Much like Clergy of the 14-17th centuries in Europe who wielded immense political influence, the AS (right or wrong) have similar authority. There is no reason to believe her actions were treason since not a single person blinked at the action.

Second ... giving the Sea Folk land in Andor is nothing horrible. As she and Rand pointed out they will have to leave the compound at some point and Andor and Cairhien will eventually profit from it ... Both the Crown in terms of revenue and eventually the commerce of these lands by having ready access to new goods which formerly would have been less available. In addition local trade just got a shot in the arm from a transportation standpoint. The fastest means of mass transit just got a permanent stop which will significantly reduce the cost of shipping to the area. International commerce is a benefit to an economy such as Andor which undoubtably will have more exportable goods than weaker or less developed countries would have. Add to that a potential source of new materials and new industries become a reality.

As to her dropping everything and running to the Amyrlins Seat... Well, so did the rest of the worlds rulers. Again, look at this through the lens of the times they are more closely aligned too ... Few rulers in the 16th century would refuse a summons by the Pope, and the incestuous ties in families such as the Borgias or Hapsburgs ran deep. Elayne is a young ruler with personal ties to the Tower and a scandal to hide both in terms of her illegitimate children and her unorthodox ascension to her throne. Open defiance to the most powerful political organization in the land would be a bad decision under almost any circumstances. For the last 3,000+ years the Amlyrlin and the Tower have been THE definitive power in the land ... To the point where legitimacy as a ruler has been a problem to those the Tower became displeased with. Granted that power has declined significantly, but as a member of the Sisterhood herself she can't very well defy the power she professes to have a piece of herself. I agree that it is odd that Elayne has chosen to side against Rand, although I have a feeling the outcome won't be that dramatic, but her going to Merrilor seems normal enough given the situation. It is unfortunate that she is gone during the attack on Caemlyn, but there is no way she could have predicted the attack via a Waygate in her city.

The Two Rivers ... Actually Elayne and Andor are the last legitimate ruling body the Two Rivers have known. She has done nothing other than ensure them protection from her Throne via the vassal they chose for themselves. And in the meantime she extended legitimacy to The Dragon by elevating him to a powerful station within Andor and Cairhien. Certainly she gains from these situations, but so does everyone in her territory. She is the first ruler in centuries to bring stability and grow her national boundaries with a shot of maintaining the growth. The odds of a challenge coming from anyone other than the Seanchan (or the Shadow) are nil thanks to her ties to the Tower. She's clearly a skilled politician rather than a despot.

Sure she's making some questionable alliances ... Aka the Kin ... But as an AS and a ruler she is in a currently unique situation and has at least been discrete enough to ensure the Kin won't engage in operations that will be certain to bring the Tower down on everyone ... As an AS Elayne can easily claim that she is simply managing the group in the name of the Tower. Yes it's bull shit, but it's enough to discourage other rulers from following suit.