Hi, thanks for your question and sorry for the delay in responding! Honestly, the flora and fauna of Riverview (as well as the architecture and cultures) are completely 'rule of fun.' The portal has been on the moon for a very, very long time, opening and closing at random, even long before the first people came through and the moon became populated, so that's a lot of time for seeds and animals to have come through on their own, let alone seeds and plants and pets and livestock that residents from other worlds and planets brought along with them.

Long story short, pretty much anything you can imagine might be found either wild or in the market, and she is more than welcome to continue with the herbalism and potioncraft, and to find whatever ingredients you'd like wherever.

In general, because of the nature of the moon and the portal, the setting itself is incredibly flexible and unless it's something world-breaking or major that would affect the game as a whole, you can pretty much go with the answer that will be most fun for you to play.