There is almost no way that anyone with an ounce of monarchical political knowledge would believe that Jisa and Treven's marriage came about the way it actually did. The theories must range wildly:
Jisa's mother Shavri used her position, both as King's Own and King Randale's lover, to ensure that her daughter would become Queen Consort if not Queen Regnant. (Very, very possible given the influence of both those positions and even likely, except for the fact that it couldn't be more wrong, Shavri was doing her best to keep Jisa off the throne)
1a. Debate ranges over how much Randale was involved, whether as a co-conspirator to being completely manipulated or too sick to do anything.
2. Randale used his position as King to make Treven marry his daughter so that Jisa would quasi-inherit even if she wasn't Chosen.
3. That one historian who is incredibly right about Vanyel being Jisa's biological father (probably not recorded in the Chronicles) and incredibly wrong about all the conclusions drawn from that. (No, Vanyel, arguably the most powerful person in the kingdom, did nothing to make Jisa queen.)
4. Treven had to marry Jisa to satisfy some court faction that supported her/bloodline traditionalists willing to overlook the out-of-wedlock part if it meant keeping Randale's direct bloodline (joke's on them).
5. Jisa seduced Treven to keep a position in the royal family.
6. What actually happened (which is probably in the Chronicles): two teens in love eloped with complete disregard for politics, they just happened to be the King's daughter and his distant Chosen heir.
