The Catholic Church does not have a required position on whether or not women need to wear only dresses or skirts. Modesty is touched on in the Catechism:
2521 Purity requires modesty, an integral part of temperance. Modesty protects the intimate center of the person. It means refusing to unveil what should remain hidden. It is ordered to chastity to whose sensitivity it bears witness. It guides how one looks at others and behaves toward them in conformity with the dignity of persons and their solidarity.
2522 Modesty protects the mystery of persons and their love. It encourages patience and moderation in loving relationships; it requires that the conditions for the definitive giving and commitment of man and woman to one another be fulfilled. Modesty is decency. It inspires one's choice of clothing. It keeps silence or reserve where there is evident risk of unhealthy curiosity. It is discreet.
2523 There is a modesty of the feelings as well as of the body. It protests, for example, against the voyeuristic explorations of the human body in certain advertisements, or against the solicitations of certain media that go too far in the exhibition of intimate things. Modesty inspires a way of life which makes it possible to resist the allurements of fashion and the pressures of prevailing ideologies.
2524 The forms taken by modesty vary from one culture to another. Everywhere, however, modesty exists as an intuition of the spiritual dignity proper to man. It is born with the awakening consciousness of being a subject. Teaching modesty to children and adolescents means awakening in them respect for the human person.
The Vatican, and many individual Catholic churches, (usually the ones most prone to tourists) have a dress code which prohibits shorts and bared shoulders.
Catholic author Colleen Hammond wrote a book called Dressing With Dignity, and has a blog by the same name, here. It looks as if the more recent posts are focusing on modest fashions on the runway, but if you look through the archive of the first year or two, you will find more substantial posts on modesty and feminine dress.
Catholic blogger Helen at Castle of the Immaculate has a series of posts on modesty. She, like Candy, came to the conclusion that she should wear dresses or skirts only. But she won't wear anything shorter than 3/4 length sleeves! I admire her dedication!
Usually on this blog, we highlight our differences with Candy. But sometimes it is nice to mention the many things we share in common, and a commitment to modesty is one of those.