I also found some information about her in Pioneers and leaders in library services to youth: a biographical dictionary, by Marilyn Lea Miller, which comes up on Google books. It says there:
When she died suddenly in 1975, Alice Brooks McGuire left a rich professional legacy built on her intellectual acumen and her uncompromising sense of values. She also left a host of friends who remembered her zest for life, her animation and enthusiasm, her contagious laughter, her wit, and her lively interest in new scenes and new activities, and above all, her integrity and great respect for all people. One close colleague, Sara Fenwick, said in In Celebration of Alice Brooks McGuire (p. 22), "To all of us she exemplified an approach to the continuity of living and learning and giving that we would cherish."If you're into vintage book stumpers or just like to read about mid-20th-century children's books, you can read quite a few of the early (hand-typed!) bulletins online. Some of the reviews are quite blunt! They kind of remind me of Anatole the mouse's cheese notes: "Excellent. Not so good. Put in cucumber seeds." Maybe they'll even help solve some long-lost book questions.
UPDATE: I figured out a way to make the bulletins searchable: use Google's site-search function along with whatever author, title or key word you're looking for. For example, "site:ideals.illinois.edu mcswigan" (no quotation marks) will bring up all the books on the site by Marie McSwigan.