I feel like I'd rather trust my wyvern than a jetpack. What if your attention is on other things going on that you forget about the fuel level?
 
[ It's not like she distrusts technology. The technology in the Free Cities is far and above anything that they've got in Fodlan and the wonders of science and innovation has indulged the lazy side of her more times than she can count. She knows that there's more advanced technology out there though (and elevator for example? She'd never take the stairs again if she had the choice) - case in point, Rocket. If not for him would she ever have gotten this up close and personal (or as up close and personal as you can when it comes to magic and imaginary) with a spaceship otherwise? 

Her skepticism, if she can even call it that, has more to do with feeling like there's comfort in knowing that she's learned how to read Waffle to the point where he becomes an extension of her on the battlefield. Well, that and Waffle has no problem telling her that he doesn't want to do something anymore. He really does take after her in a lot of ways. ] 

Hey - would you want to try and fly Waffle? I'm sure it's not as fun as having a jetpack, but it's probably a lot less tiring. 

[ How exactly she doesn't know but she's really trying to entice him here. ]