There is a stray cat outside my school and she is thin and malnourished (even though I feed her everyday) and I noticed her stomach has gotten a little big. She doesn't trust me to let me touch her but she comes near me. Could she be pregnant? How can I be sure that she is/isn't?

Chances are that a stray female cat is pregnant. She could have worms or parasites. Very sad. Feral cats won't let anyone touch them.