The reason why it's Jenny is because if Edith did not swim more laps that Shira but more laps than Gemma, that means Edith is second to last. Gemma is last because she did not swim more laps than anyone. Jenny would have swam the most laps out of the four girls.
Lets take this step by step. If Edith swam fewer laps than Shira but more than Gemma, then G < E < S. If Jenny swam more than Shira, then that means Gemma swam the fewest, then Edith, then Shira, and finally Jenny who swam the most laps.
