(i) The fetish kicks me out?it’s like a pointless “oopsy daisy” that undermines the story.

(ii) Adding the word “reluctant” does not justify the protagonist’s moral choices. If you want us to feel for her, you need to give us more background.

(iii) How would her staying young help her daughter? Do you mean that if she stays young, her husband will not divorce her and her daughter will not grow up without a father? Is this strong enough a reason for someone to turn into a killer?

(iv) I agree with the other comments: why does she have to kill people with her own hands? Do you visit the rejuvenation clinic bringing in your own victims’ blood cells? Does her husband not pay for the operation and must she find her own way to do it?

Arbitrary attempt to re-write the log line ensues. Let’s study the formula:

(0) WORLD SETTING:
“In a society where science helps privileged conservatives stay young by sacrificing homeless children,” (or teenagers)

(which explains the social structure and the sci-fi premise)

(1) BIG EVENT:
“when her husband files for divorce on the grounds of her old looks,”

(which hints the society’s patriarchy)

(2) FLAWED PROTAGONIST:
“an neglected housewife”

(3) MAIN ACTION:
“becomes a serial killer to finance her rejuvenation and save her marriage.”

(OK, how killing people finances the rejuvenation is not clear, but I don’t know what your intentions are down that road.)

Now, this would only work if the “centre of good” is on the homeless victims and not the protagonist killer with her absurd privileged problems. I very much see this woman being punished in the end.

The question is: is there any character that embodies the good? Perhaps a homeless vigilante? A Hobo With a Shotgun type?