Henna actually isn't cultural appropriation. I'm Omani and a quarter Yemeni, so its also a part of my culture. For the most part, henna isn't worn for spiritual purposes anymore, but rather as a fashion statement. Although it was originally a part of Hindu tradition, it also spread to other areas where the original symbolic meaning was lost. Also, henna is the Arabic term, and mehndi is the term used in India, so only the latter term should be used in the context of Hindu temples.
Snaps to you! Thanks for the knowledge.