sounds like my girl's cot. by the way at 10 months we dont't use cot bumper anymore. cause like you said they flip here & there and the cot bumper dont't cover the sliding railing so we thought no point.
she will kick the railing, get her leg stuck in between and we can find her in the morning with her legs dangling through the railings out of the cot.
kids are quite hardy so even if we think it's very painful actually it's nothing to them, especially if your girl doesn't cry from the kicks.
my girl is now 15 months and her legs looks normal to me and she is walking normally too.
i think if you put a pillow there somehow in the night she flip here and there kick here and there the pillow will be removed from its position. but like you said what if it cover her face? so i think it won't solve the problem also.
if it is affecting your girl's sleep i think eventually she will learn not to get too close to the railings at night. Now my girl still flip here and there in her sleep but she seems to subconsciously know the boundaries so she dont't really sleep very near the railings anymore.
dont't worry too much.