@Jennifer1596 There is no strategically sound reason to offer a refund to this guest. I think your suspicion is likely correct: the guest had no intention to stay in your home overnight, and believed she could scam you into free use of the barn as a rest stop between hiking and returning home. I would not return a penny to this guest, and I'd also leave an honest review warning other hosts of her poor behavior.
How to stop this from occurring again? I'd start by increasing the minimum stay. One-night stays are just not worthwhile given the amount of effort required to turn over (especially if you're actually following the enhanced cleaning requirements) and the heightened risk of problem guests. If you're not using Instant Book, a bit more correspondence before accepting a request can usually give you a good feel for the guest's motives and appreciation for your listing. People who are charmed enough by it that they'd like to stay for three days or more will probably be your ideal target customers.