You need to find a middle ground with your mother in terms of accepting and respecting her religious beliefs while working to convince her that there is no use being superstitious. Through a years-long, repeated and constructive dialogue on this subject and especially through your overall attitudes and behavior, you will also manage to convince your parents that despite lacking conventional religious belief you already are, and will always be a good, reliable and conscientious human being.
As an Indian living in India I am intimately familiar with the family situation in your question. I admire your having the strength of your convictions on this complex subject so early in life, but many people have 'found religion' in the most unexpected ways later.
In September I actually asked a question on this site about how to handle a religious uncle who assumes that I am similarly religious:
How to deal with a religious relative who keeps assuming that I am similarly religious?
I have recollected what I posted in a comment on that page:
It's easy, especially in India, to pretend belief and 'go with the flow', which is what I usually do for unavoidable religious occasions.
Because we will eventually learn that honoring the generic religious life of the land and respecting other people's religious beliefs (including your mother's) is socially expected and culturally more important than our own personal faith or lack of faith.
India has many religions and is a predominantly religious society; and I come from a generically and conventionally religious family. Indian women belonging to any faith are likely to be especially religious because men are expected to be the pillars of the wider social community but women are expected to be the real pillars of the religion and its rituals, and also teach their children to have strong and unquestioning religious faith.
However my belief in religion was lukewarm to begin with and faded out completely by the age of 24, mainly because I had seen the harsh realities of human existence all around me and had no experience of the 'divine grace' to give depth and strength to socially acquired religious beliefs.
I then passed through a one-year-long phase very similar to what you have described here, when I resented having to take part in religious activities that I did not believe in, as directed my mother who is a very religious person. That phase was 12 years back and my parents eventually discovered my lack of religious belief. Luckily my father is not too religious himself and believes more in human goodness than rituals; and my mother was gracious enough not to make it a big issue of constant friction between us.
In turn I had the good sense not to rebel overtly myself, and eventually settled into a pattern of doing my 'religious duties' in a mindlessly token manner with my parents tacitly accepting my lack of belief. However I managed to find a middle ground with my mother by stressing the value of religion's ethical and moral teachings while explicitly discouraging superstition. I also learned to appreciate the social and psychological value of religious messages without taking extreme exception to what I still consider intrinsically meaningless rituals that however serve many social purposes.
It was for me and it is for you a good opportunity to learn the art of compromise. Superstitions and rituals are deeply embedded in certain religious cultures and it will not be easy to convince your mother because a superstitious person sees it as reality and not as superstition. It can also take years to get your parents' genuine acceptance of your being an unbeliever because Indian society heavily emphasises a religious life and your parents being orthodox will face a cultural challenge to accept your lack of belief.
The first 'heart to heart talk' on the topic with your mother, as advised in an earlier answer, will only serve to establish the foundation for a years-long running conversation on the issue. However it will eventually be a rewarding dialogue because we can influence our parents in positive ways and I can report that my mother has eventually become not at all superstitious and she is now a quietly, sensibly religious and spiritually very strong person.
Our morals and values are acquired not from religion as such but from excellent and ethical role models who are mainly our parents. Since Indian parents typically worry how their children will manage in life if they don't have the support of religious belief, it is your job to keep working constructively to convince your mother that despite lacking religious faith you are already being and will always be a good, reliable and conscientious human being.
You might also have to learn not to overly proclaim your atheism to the local community at large, now and in future, wherever you live now and wherever you may go later. Keep your unbelief in your own mind and do not challenge orthodoxy. Religion is taken very seriously in many parts of India and by Indians living in many parts of the world. So too in many other nations and cultures. Your unbelief is your own business, but you will soon learn to tolerate some token display of religiosity in order to purchase peace and keep a low profile, so that you can concentrate on achieving what you really want in your life!