Complex sentence: She previously stayed over at Alice's home in England, although she herself is rather bad at English and has generally bad grades.However, when she suddenly gets inspired to study hard, she could do a lot better than Aya.
Split into simpler sentences: She previously stayed over at Alice's home in England, although she herself is rather bad at English and has generally bad grades. However when she gets inspired to study hard, she can do a lot better than Aya.