Your daughters problem is not uncommon. Children tend to compare themselves with each other. Some children who may be from families that are newly rich, try to establish that they are superior, because they are rich. This is not true, of course. What you should tell your daughter is that it is important to be a nice, helpful and kind person and to be a good student who is interested in learning new things and willing to share both time and knowledge. I have taught generations of students and can tell you that these qualities (along with a sense of humour) are the qualities that are most liked.
Showing off about being richer is something that will disappear as the children grow more mature. You should tell your child that the great success stories in our own times are those of people with humble beginnings, who worked hard. Our President, Abdul Kalaam grew up as a boat-makers son and studied on scholarships and our Prime Minister, Manmohan Singh was from a simple farming family. See where they have arrived and how much respect they command around the world. You must feel convinced about the true values and talk to your daughter not to bother about petty comments from her classmates. Since you mention that it is a reputed school, you could also talk to her teachers and have them establish the right values in the school.
Finally, some of these things will not go away and your daughter will have to develop her own methods to deal with them. Have the others in the family also help you in dealing with this.