In 1994 the Church allowed bishops to give permission for girls and women to be altar servers within their dioceses. If a bishop of a local diocese allows the practice, parents may choose to allow their daughters to be altar servers. It is also within the rights of a parent to not allow his daughters to be altar servers. The Church does indeed still very much recommend that boys should serve at the altar:
It is altogether laudable to maintain the noble custom by which boys or youths, customarily termed servers, provide service of the altar after the manner of acolytes, and receive catechesis regarding their function in accordance with their power of comprehension. Nor should it be forgotten that a great number of sacred ministers over the course of the centuries have come from among boys such as these. … Girls or women may also be admitted to this service of the altar, at the discretion of the diocesan bishop and in observance of the established norms (Redemptionis Sacramentum 47).
That said, it seems that you have already given your daughter permission to be an altar server and are considering revoking that permission based upon a personal ideology. It is within your rights as a parent to do so. Could it be though that you could have thought through your position more carefully before giving permission? Would it be just to your daughter to penalize her now for a neglect to do so (particularly since the Church itself has no problem with your daughter’s altar service)?
Finally, what is the situation at your local parish? Do boys now serve at the altar? If you remove your daughter from the program, is there a likelihood that she will be replaced by a boy or will she likely be replaced by another girl? If she is likely to be replaced by another girl, what would be the point of removing her from the program?
Whatever you decide to do for your daughter, it seems to me that if a feminization of parish life bothers you, then perhaps you should consider your own level of commitment in parish life and ask yourself if there is more that you can do. Options for service include becoming a lector, an extraordinary minister of holy Communion, an usher, a catechist, or a parish leader. Perhaps your involvement in parish life may inspire other men to follow your example. When problems like this crop up, our first thought ought to be given to what we ourselves can do to make a difference. After that is done, then it makes sense to consider what we can ask our families to do to pitch in as well.