Just Google and you will find many, many links. I give you a few here:
Probably a variant of Nirjana, which means in Sanskrit and Indian: "Spotless, pure":
http://babynamesworld.parentsconnect.com/meaning_of_Niranjana.html
According to others Nirjanjana comes from the Indian word meaning "Goddess Durga":
http://www.birthvillage.com/meaning/Niranjanahttp://www.babynology.com/meaning-niranjana-m30.html
Other links:
"pure and free from falsehood"
http://answers.yahoo.com/question/index?qid=20060716005744AA9487gName Of A River; Goddess Durga; The Night Of The Full Moon:
http://webcache.googleusercontent.com/search?q=cache:xPZj6a6obPkJ:indiannames.returningtoindia.com/linkdetail.aspx%3Fid%3D720+meaning+of+niranjana&cd=8&hl=nl&ct=clnk&gl=nl
However the most plausable explanation I found here about the name Niranjan (of which Niranjanna seems to me to be a female variant):
"Niranjan is one of the names of Venkateshwara, a god in Hindu religion. Niranjan is another name/form of Lord Shiva.The literal meaning in Sanskrit is "Fearless".(Nir=Without;Anjan=fear; in Sanskrit "Anjan" means "MAYA" as in the causal force for all feelings of "self" and belongings. the word being a porttmanteau in sanskrit means one without blemishes [anjanasya abhavaha]":
http://wiki.answers.com/Q/What_is_the_meaning_of_the_Hindu_name_Niranjanhttp://askganesha.com/babynames/babyname.php?id=Niranjan&nam=N