How do Ifemelu, Obinze, and Aunty Uju undergo character development?

The quality that unites these three Adichie characters might best be defined as "grit." Each of these characters is singular in their talent, idealism, and hope. They all have talents, such as writing or medicine, and are able to maintain momentum and motivation even though they are all brought incredibly low at varying points in Americanah.
Aunty Uju has much to offer and continues to push forward despite not being sufficiently valued in either Nigeria or America. She uses the financial security of depending on powerful men to protect herself and her son. It is not surprising that she is a character who is most constant in Ifemelu's life.
Obinze is also nearly destroyed by his time in England, as his hopes and dignity undergo incredible abuse. Rather than living the life he dreamed of, he is forced to clean toilets and to live as a disrespected immigrant, where his intelligence and gentleness have no value. Similarly, due to poverty, Ifemelu is brought low in Philadelphia and is almost forced into taking up sex work. She is forced to confront her blackness, and therefore her perceived inferiority, in America. From this assault on her dignity as a unique human, she constructs a successful blog that brings her closer to her initial ambitions and, ultimately, back to Obinze and Nigeria.