I'd say save up Coupons until an event comes, but if you're still in the early numbers, just build up fragments from events like the star wheel. You might get lucky and pull her from the lucky wheel or something if she's on another, I've gotten her on the wheel once on another server I play on. On my main server, I just collected frags from free events and bought her in sage treasure, but was pretty expensive, being at 800 coupons.
But, as many others have already said, she'll be coming to the shops soon, so I'd also suggest just waiting. You c*so grab fragments from survival breakthrough every now and then. Good luck, hopefully you'll manage to get her soon. Don't use your scrolls on seal, the chances are slim, and there's not much to get from there, I'd suggest either saving your seal scrolls for Jinchuriki treasure, or using them on a current treasure. Once again, good luck.