In the past women composers were rarely mentioned in music history books and textbooks. Here are some quotes that were discovered when examining UAH's music collection.
“In America the work of women in music has an especial interest, because the absence of all prejudice against women composers has led to a larger number of female writers of music than is possessed by any other country.”
From the book Women in music by Louis Charles Elson. Published by the University Society, New York, in 1918.
One music history textbook published in 1941, Music in Western Civilization by Paul Henry Lang (W.W. Norton & Company) contained very little information on women composers and musicians.
On page 31 Lang wrote, "The monkish theology of the early Middle Ages belittled women and considered them the most pliable tool in the hands of Satan”. Lang wrote on page 302, "Musical organizations founded and conducted by women were numerous, especially in Italy, and the religious in almost every convent were devoted to music”.
Another popular music history textbook, History of music and musical style by Home Ulrich & Paul A. Pisk, published in 1963 by Harcourt Brace Jovanovich, briefly mentioned Clara Schumann as a musicians but nothing about her compositions.
In Music Reference and Research materials: an annotated bibliography, 3rd edition, compiled by Vincent Duckles, published in 1974 by Free Press, only one book was listed in the subject index that covered women musicans and composers.
By the time the 5th edition (1997) was published, the Music Reference and Research materials: an annotated bibliography, by Vincent H. Duckles and Ida Reed, had a larger listing of women in music in the subject index.
A history of western music, 7th edition, by J. Peter Burkholder, Donald Jay Grout, Claude V. Palisca, published by Norton, 2006, has expanded its information on women composers.
Information on individual composers such as Joan Tower, Hildegard of Bingen, Clara Schumann is provided with examples.
Nannerl Mozart (older sister) (Maria Anna) - “When she became of marriageable age in 1769, she bumped up against the prevailing attitude that women belonged at home. Accordingly her father insisted that she stop performing in public, and she was left behind in Salzburg…” page 551
Fanny Mendelssohn Hensel - “Few pieces were published in her lifetime, because her father and brother opposed publication on the grounds that a musical career was inappropriate for a woman of her class”. page 619
Music an Appreciation, sixth brief edition, by Roger Kamien (Mc-Graw-Hill, 2008) is a textbook often used in Music Appreciation classes.
This book contains examples of women composers from Hildegard of Bingen, Clara Weick Schumann, and 20th century composers.
"In the twentieth century, more women than ever before became active as composers, virtuoso soloists, and music educators.” “And in the years after World War II (1939-1940), women joined professional orchestras as instrumentalists and conductors.” Page 303
Here are just a few suggested books and databases that will help you get started with your research.
Baker's Biographical Dictionary of Popular Musicians Since 1990 by 
From convent to concert hall : a guide to women composers by 
Towards a Twenty-First-Century Feminist Politics of Music by 
Women's Voices Across Musical Worlds by 
Women, Music, Culture by 
Women and Music by 
Women Composers and Songwriters by 
Women in music : a research and information guide by 
Featuring digitized content from 1970 to the present, the Music Index contains cover-to-cover indexing and abstracts of articles about music, musicians and the music industry for more than 480 periodicals. It also provides selective coverage for more than 200 periodicals.
The Naxos Music Library is an on-line library of more than 75,000 tracks of music from the catalog of Naxos, a leading classical music label, and selected additional labels. Although Naxos is best known for its classical recordings (with more than 200 released each year), the Naxos Music Library also includes world music, jazz, and national anthems. All of the Naxos repertoire may be searched in standard/advanced modes or browsed in a large number of categories and genres. In addition, Naxos offers a number of text resources including overviews of music history, program notes for recordings, and the complete libretti of operas available in the Naxos Music Library.