The holy alicorn goddess takes divine baths at her castle, able to cleanse herself of every single dirt, grime, germ, ill substance and the like with very little effort, leaving her body and fur always pure, clean, and white as snow. She'll even on rare occassions allow her guard to partake in once in a lifetime barhs with her which they immediately accept without hesitation.
However, a certain purple alicorn bookworm was very displeased to find out that Celestia had intimate fun with the mega-sized Changeling giantess without inviting her. She at night caught a small glimpse of Celestia teleporting to her bed chambers to shower while noticing a hint of green saliva in her mane. Poutful blows directed towards the goddesses' chest are only arousing her more than doing any bit of harm (which is what Twilight wanted). Twilight wanted to use that chance to study how it would feel to have an interspecies relationship with a Changeling, already having all of her needed scientific equipment for data analysis, but was too late. She was only interested in the Queen herself, not any soldiers of her army. Celestia is required to bring the young nerdy alicorn with her the next time Chrysalis offers herself up again…which is rare.
Here's an aftermath view of Celestia's encounter with Chrysalis followed by an angry Twilight who wanted in on it.