You know, I just cannot /not/ see Myriah having some hand in whom Baelor married since Daeron seemed to be hellbent on getting him a Marcher bride. Myriah would want to make sure that Baelor didn't wake up with a blade to his neck in the middle of the night.
I know with the Marcher Houses, while they're all old, some are older than others. The Swanns and the Carons? Far more powerful. Much older than the other houses. The Dondarrions are old (they started out as an Andal House, not long after the Andal invasion, and a Durrandon King formed their house and granted the first Dondarrion Blackhaven (that's the tldr version of it)). But i always saw the Dondarrions as having a great deal of political capitol? Like maybe they're a very well liked house in the Marchlands and the Stormlands at large, and as such they have tremendous political capitol because of that. And overall they might not have been as...openly violent about their anti dornish sentiment at the time that they were looking for a bride for Baelor.
But since I think there's no way Myriah wouldn't have had an influence in whom Baelor married (as much as I like the idea that Baelor did have some of his own choice in the matter), I wonder if she actively picked House Dondarrion, or her and Jena had encounters or - who knows what could have happened.
I also like the idea that the Daeron and Myriah started poking around during Daenerys and Maron Martell's wedding. it was said the entirety of the realm was invited in the name of unity. Maybe Myriah said to Daeron (basically) that 'I hate this idea but since you're determined, we are doing this my way.'
(I also am admittedly into the idea that maybe they met at Daenerys and Maron's wedding and Baelor had to crown Daenerys as the Queen of Love and Beauty when he won the tourney and earned his nickname since it was her wedding but if he had it his way, he'd have crowned Jena.)
mmm i'm so into every point here... my personal headcanon is that baelor is the BEST kind of mama's boy and of course myriah would know what kind of lady he'd be into. and i think for both myriah and daeron ii like... that's their beautiful boy, yeah they're gonna need to make a political match but they also want to find him someone he's gonna be happy with (happy wife = happy realm & so on). so yeah i still think that all of their sons' marriages were arranged but i think they cooked with baelor/jena and with maekar/dyanna in particular (rhaegel/alys seemed fine? functional? do NOT know wtf they were thinking w aerys/aelinor though)
also this is canon jena to me:
