Therese, the oldest, is seventeen. Our first glimpse of her isn't very flattering:
Therese Lisbon had a heavier face, the cheeks and eyes of a cow, and she came forward to meet us on two left feet. (1.42)
Unlike some of her sisters, she's not much interested in girlish things. She helps her dad with yard work in man-like clothes, boots, and a cap. And Therese is something of a science nerd; she wears her protective goggles from lab class in the hall and grows seahorses in a drinking glass in her bedroom. She knows about all kids of things, from the Doppler effect to Dutch Elm Disease. She does science experiments, is in the high school Science Club, and keeps a stuffed iguana with fake organs that she uses to teach people about anatomy. Her Spanish teacher remembered her as a smart girl with an amazing ability to memorize Spanish vocabulary, but her ability stayed at the intellectual level:
"She could speak Spanish," Mr. Lorca said, "but not feel it." (3.7)
Therese is also a ham radio operator, which the boys see as her attempts to reach out to the world beyond her prison of a house:
"What is Colombia like?"
"Warm. Peaceful. Come."
"Like to. […] Have to go. Mom calling."
[…] The interpretation is, we think, quite obvious, and shows that as late as March, Therese was reaching out toward a freer world. About this time she sent away for application materials from a list of colleges […]. (4.78-4.80; 4.86)
Therese had once told one of the boys, "We just want to live. If anyone would let us" (3.189). But no one does, and Therese never makes it to Colombia or to college. She overdoses on pills washed down with gin and dies on June 16.