Complex sentence: She fell in love with it and begged her mum allow her to give up competitive swimming to do the two classes each week, which quickly led to doing two sessions a day and spending all her time training on her own between these sessions.
Split into simpler sentences: She fell in love with it and begged her mother to allow her to give up competitive swimming to do the two classes each week. This quickly led to doing two sessions a day and spending all of her time training on her own between these sessions.