Can I use a postpartum peri bottle as a travel bidet?

Yes, and many people do. Postpartum-focused reviewers in r/BabyBumps and r/beyondthebump describe keeping their peri bottles long after recovery specifically for use as a low-pressure portable bidet. The trade-off is that peri bottles are tuned for gentle rinsing, not aggressive cleaning, so they're a great fit for sensitive use cases and a weak fit if you want strong pressure.