Swollen or puffy eyes can be the cause from 2 things. Its either poor water quaility, or a Vitamin A deficiency. What are the turtles housed in, do they have clean filtered water? If not the owner needs to invest in a GOOD filter. Also, what are the turtles being fed? They should be given a varied diet. One thing should not make up the turtles entire diet. Feed a good pellet food such as Mazuri or Zoo-med. Then on the side, give them feeder fish and aquatic plants like Anacharis. Sounds like this girl is pretty young. Turtles are not a good choice for a young child. They are expensive and require a lot of work to care for properly.
Chris
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0.1 Red Eared Slider, 1.0 Common Snapper, 1.0 Bearded Dragon and a 55gal Native Fish Tank with a 6in LM Bass, 3 Crawdads and a Pleco.
I use to have a collection of Leopard Geckos that I bred, but have sold them.