It is just that since she was shown to be cheerful kid happy with what little she got and doesn't let her troubles and problems spoil her mood and happiness people think that she is content with life.
It is just that she doesn't let the darker side of her life affect her or people who care for her like her teesa Kamili.
It was shown many times how she thinks about her mother especially whenHarki's taunts her with *thari maa* or when she hurt herself she used to ask herself why she remembers her mother when she didn't even what she looks like and why Maasa's picture doesn't come into her mind when she thinks of Maa.
Then there was heart wrenching scene after she saw how Urmi's father treats Urmi how she considered herself all alone having no family of her own.
Just like people that Anandi doesn't feel enough pain about her lost daughter they thought Nandini also never missed her mother.
Being angry and hating her mother is not the same as not missing the need for her mother.