Yara is a born leader who inspires confidence in her followers and makes smart decisions. She is the epitome of what a good queen should be—which is precisely why I don't believe George R.R. Martin will let her survive to rule. Yara and Robb display much of the same qualities in their personalities, although Yara appears to be much more savvy when it comes to betrayal. She managed to anticipate her uncle's actions at the Kingsmoot and escape him, for now. Like Robb, she's negotiated deals she didn't really like, and that may end up hurting her in the long run. We all know how Robb's treaty worked out for him, and I don't think Yara's will end any better. One crucial thing I noticed is how casually she negotiated away the Ironborn way of living, through raiding and reaving. The Iron Islands are primarily rock, and the Greyjoy words "We Do Not Sow" should be taken literally—there really isn't anywhere for the Ironborn to cultivate much food. This means that Yara has sentenced the Ironborn to a life of struggling to survive on fishing, shipping cargo, and other related trades.
For now, Yara is Queen of the Iron Islands—as soon as Daenerys assumes the Iron Throne—but ultimately, I think her role is to be a sacrifice along the way for Theon's final trial. As an audience, we haven't really seen enough of Yara over the last six seasons to really care much about her or become invested in her success. To me, this is another indicator of her impending demise.
If Yara is the one captured by Euron, as seems likely, I don't think she will survive long. Theon will be motivated to rescue her, but I think he will be unsuccessful. The most likely scenario is that Euron pulls a Mad King and sets up a situation where it's impossible for Theon to save her—much like what happened to Brandon and Rickard Stark—and Theon ends up witnessing her die before his eyes. This final blow—the death of the one family member who never abandoned him—will be the ultimate trial for Theon. Will he crawl back into his hole of self-loathing and give up? Or will he rise again, harder and stronger, to get vengeance on his uncle and take back control of the Ironborn?