...how do people trade with them, if it's a secret?

You go through a broker or know a guy, apparently.

Where can she find a broker? Where can she find a guy?

Go to a tradebroker's office and make an appointment! Nils probably fits the bill for the second thing actually...

Ooh, Nils, yes. She should call him.

Hey, Nils?

"-ou back in ten minutes okay? Finishing core integrity enchantment alteration." Click.

Ten minutes flying she can do.

Eleven minutes fifteen seconds.

Her crystal chimes back up for him. "Glad that's done. I'm making great time on the upgrades. Hello."

"Hiya! How're you doing?"

"I am greatly enjoying the ability to work on a project I have been planning in bits and pieces for years with minimal budget or time concerns."

"Glad I could be of help."

"Good! How's Suvak?"

"Fun! I met some fair folk and also happened to run into my soulmate."

"Wait what. And hold on - your voice is different, but okay you demonstrated that capacity well enough, nevermind, and you mentioned the mate thing. Erm, big news."

"Yeah, I'm a girl today, and yep, mate thing. Took me a bit to realise, but I've heard of people taking days so all in all I feel lucky."

"...Congratulations?"

"Thank you!"

"I feel like I should be making a bridal shower gift for some reason..."

"Oh, marriage, that's a thing. Wow I hadn't thought of that that's a great idea—but he's not in love with me yet, nor a vankire."

"I would find your current situation really stressful. Hearing about it happen is a point in the 'no way vankire' column."

"It's stressful, yeah, but it's also really really great? And a centaur told me he'd become a vankire eventually, too, so that's good, he won't die in the meantime. And he'll love me as much as I love him, but I kinda want him to love me before the magic sets in."

"I have done my best to avoid... Romance. I wouldn't know."

"Well, are you asexual? Or aromantic? 'Cause if you are you probably won't get a mate."

"I am not, I'm just a sarcastic loner type who gets tired of most people really easy. Well, maybe the second thing, I don't actually know how to tell."

"Your mate is, as far as anyone knows, guaranteed to be someone you'd actually get along with and love and be compatible with even absent mate magic."