You know, I've loved Project Hail Mary for years, but it wasn't until (post-movie) i connected with the Tumblr fanbase, and saw all their empathy for Stratt that I realized...
She's a symbol of Mary. She brought Grace into her project to save the world. She knew he needed to be sacrificed to save humanity. She loved him and she knew her final decision would really hurt him, but she did it because his sacrifice was what the world desperately needed.
There's a lot of symbolism with Grace being the savior who doesn't want to but, when it comes down to the wire, ends up sacrificing himself to save everyone. But I hadn't realized the role Stratt played in the allegory.