From the look of it, neither of them were THE country’s royal heirs before becoming King and Queen because they were the one to create the modern idea of Spain and it’s monarch line. And for a society so patriarchal, it’s more traditional to label her husband before her right? I’m confused why I see so much attributed to only her or with her in front of her husband. I thought maybe it was just internet being the wild west, but even Wikipedia does it.
Is this a case where, excuse my wording, she’s reached “girlboss” status in our modern eyes or was she the real ruler behind her husband? Or were they allowed to equally rule the country thus got credit for the work they put in?
Isabel was the queen regnant of the Crown of Castile, which was four times the size and four times more populous than king Ferdinand's realm, that's the main reason why Isabel is regularly listed first.
Heraldry also plays a part on the matter. It is something extremely visual, and it gives a quick reading if one knows how to do it. In the case of the Catholic Monarchs' heraldry, the arms of Castile take precedence over the arms of Aragon, occupying the first and fourth quarters of the escutcheon, whereas Aragon's arms are on the second and third quarters.
This was one of the many things settled on the Concord of Segovia, which established how power would be shared in the Crown of Castile: Isabel was the proprietary queen of the realms of Castile, Ferdinand would be styled as king, have command of the armies, and have his voice heard in the realm's matters, though the queen would have the final say. Castile's arms would take precedence over Aragon's, but the king's name would precede the queen's name.
So, long story short, for matters relating to Castile, Isabel gets mentioned first or even alone in historiography because she was the proprietary queen, and had final say on all matters. Conversely, when writing about matters pertaining to the Crown of Aragon, it is perfectly frequent to not mention Isabel, as the proprietary king was Ferdinand.
Do also bear in mind that the union of Isabel and Ferdinand did not result in the formal unification of the crowns. The realms of Aragon and Castile had different laws, measurements, coinage, there were customs between them, etc. One of the most famous instances of this lack of unification was when disgraced royal secretary Antonio Pérez fled Madrid when accused of treason: he took refuge in Aragon, where he was outside Castile's justice's reach. For lack of any better options, Philip II had Pérez accused of heresy by the Inquisition, as the Inquisition operated both in Castile and Aragon.
Forgot to mention that Ferdinand was the heir of the Crown of Aragon back in the day, an undisputed fact. Isabel was the heir of Castile at different moments, and eventually took the crown after defeating Juana "la Beltraneja" in the civil war.
It would be helpful if you could give an example of what you mean, as in casual usage there are plenty of uses of "Ferdinand and Isabella" rather than "Isabella and Ferdinand". However, I think it's necessary to make the point that while they achieved a personal union of Castile and Aragon, they didn't create "Spain" as a unified entity - Isabel was queen of Castile and Fernando was king of Aragon, and they each ruled their own realm. This may play into what you're seeing, if for instance it's a reference to something pertaining to Castile.
I have a past answer on this that may also help you: How would Royal marriages work, in respect of governance, when the two participants were both ruling monarchs in their own rights?