I've just been mulling over the options for an intro.
The thing is she doesn't have connections or the like with anyone of any importance. Or anyone at all for that matter. Plus being demi-human and not really showing much care to hide it. So after some thought, I'm thought of a potentially funny (at least to me) way to introduce her lol

She's been following them for a little. After hearing the stories, she heads to the capital, manages to track them down and catches them defeating Rayla and is subsequently satisfied that they're at least strong enough to help get her vengeance against the waves. So she follows them back to the capital again, all while staying hidden. Though I imagine Marcino was aware she was tailing them the whole time, it's not like she's a massive threat to the party level wise lol

Once back at the castle however she has to sneak inside, and against regular guards she can probably get in easily enough, however she gets caught out at some point and is restrained/captured. Pretty sure there's more than enough people in the castle who can detect and easily capture her lol

Then when they find out her only objective is to join the heroes party and fight the waves, they decide why not. She's at least somewhat capable and useful, so at least give the heroes the option of letting her join. [s]And who says no to free floofy tail and ears right?[/s] In which case, she can already be in the throne room or wherever waiting.

The other option I've consider is she just beats up some guards and barges in to demand being in the party lmao She has a pretty simple thought process for such things.