She doesn't notices....at first.

Having just know barely survived almost getting drowned in the ocean, Petra's first action upon reaching the shore, was making sure she didn't had any injury, and for that end, she began to check with her hands the state of her arms, legs, back, face and navel, but not the bikini area, as she didn't want to loosen the makeshift swimsuit.

"Good thing everything's fine...", exclamed Petra to herself as she finished her checkup, "Oww, my sandcastle..." she moaned as she looked at the mount of sand that was once her own creation, upon which, she remembered something important.

"Wait, i should probably go and see if everyone's fine...", she commented, after which, she began to walk across the beach shore to where her classmates were located, completedly unaware that she was completedly naked from head to toe, not helped by the fact that she wasn't an stranger at walking in the beach naked.

"Dorothea!, Edelgard!, Everyone!, are you fine ?!", she yelled loudly as she traversed the sands of the isle, waiting for a response, until at last, she encountered the sand and sea weed covered figures of her classmates emerging from the ocean.

"Oh, there you are!", she exclamed happily as she approached them, "I was dead-worry something happened to you!", she said as she helped her friends get off the water.

"uhrrhhg, thank's Petra!", replied Dorothea as she got on land with her help, and wiped off the sand from her eyes, upon which, the first thing she noticed were the brown bare boobs of her classmate.

"Petra, your...", Dorothea said to Petra in the most politedly way she couldn't as she pointed her hand towards her bare breasts, after which, Petra inmediatedly realized what was her current state of clothing, or rather, lack of therefor.

"O-Ohh, e-ehhh....", she said in a shyly tone, for she was now fully aware that she completedly bare naked in front of all of her classmates, who despite their sorry state, were still dressed in their swimsuits, which made Petra even more self-conscious about her nudity.