We don't know that "people" were not called back. We know that one employee was not called back and that she is over 40. That's hardly enough to support a claim.
True story. Former employer ran an ad for a job opening. We had multiple applications, and we hired the best person for the job, who happened to be over 50. Several months later, a new position was created internally, she applied for it and got it. We ran an ad for her old position. One of the applicants, all of a sudden, screamed (during the middle of the interview), "I remember you people now! I applied here once before and I didn't get the job! You discriminate based on age!" and stormed out. She was AT LEAST ten years younger than the woman we hired.
Point being, there could be a dozen different reasons why the OP hasn't heard back, including that they're still reviewing resumes. It's WAY too early to assume that her age has anything to do with it.
And there's nothing illegal about letting higher-paid workers go in favor of lower paid ones.

