Okay, so: Natasha doesn’t usually have enhanced physical abilities beyond slowed aging, and Yelena was introduced when Black Widow didn’t have any powers at all. Pale Little Spider was a Yelena origin miniseries and there were no chemicals or serums involved, just intense physical training. Keep in mind that Yelena’s first appearance was in 1999, when it was still pretty concievable that Natasha could be the generic mid-thirties superhero age and still have been trained before the fall of the USSR in 1991.
In the original stories, Yelena operated under the auspices of the GRU, not the KGB, but there was implied institutional carry over. Yelena mentions Natasha’s test scores and constantly compares herself to the Red Room’s greatest student; Natasha knows Stalyenko, Yelena’s handler. Anyway, from these early appearances— it would be pretty straight-on to assume Yelena recieved the exact same training and even had some of the same teachers that Natasha did. And because this version of Natasha didn’t have any powers or treatments, this first, essential Yelena didn’t either.
Then things got complicated. Natasha suffered a series of retcons and unretcons that has made my job of explaining them much harder, and Yelena has never been written consistantly again. So!
Richard Morgan was the one who introduced the idea of “biochemical enhancements” into Black Widow canon, which in his stories were mostly cosmetic— Natasha didn’t get sunburned, her hair didn’t fall out, things like that. (Morgan’s Natasha might have aged more slowly, but she was specifically in her late thirties, not her late seventies.) Morgan was very clear that the ~real~ Red Room continued as 2R, a KGB splinter group, and was not the same thing as the Red Room that trained Yelena. Subsequently, the biotech that the original Black Widow operatives had was still the property of 2R, not the contemporary Marvel Universe GRU.
Yel—? Oh— her. Oh, my goodness, no. Belova was a, an aberration. Nothing to do with the real Black Widow program. I believe she models fetish lingerie these days.
I don’t think Morgan liked Yelena very much!
The next retcon, which happend in the late 2000s, established that Natasha got her aging slowed by a mysterious “chemical”, but doesn’t have any powers otherwise. This timeline locates Natasha’s Red Room training back in the mid 1950s, separating her graduation from Yelena’s by more than five decades. At that point, I think it’s pretty likely that the instruction Yelena had differed from Natasha’s signficantly. She might have gotten the same chemical treatments, but I’d say probably not.
But wait! Yelena has a whole other powerset that has nothing to do with all this.
Sometime off-panel, Yelena joined up with a rogue cell of SHIELD agents, who encountered the New Avengers in the Savage Land. Yelena was burned to a crisp by the Avengers team, but she was rescued by HYDRA, who turned her into a Super-Adaptoid, which is a kind of robot powered by the Cosmic Cube.
This is what I have to offer. Behind me are the greatest minds of Advanced Idea Mechanics. AIM has been working with us to better our cause. What they’ve been able to do is sythesize— they’ve synthesized this adaptoid’s unique biology. They know how he works. They say they can make you as powerful and beautiful as you deserve to be. You can strike back at these rebel heroes using their own powers to beat them… So… what say you, Black Widow?
As Super-Adaptoid, Yelena could absorb and copy powers, and she gradually turned into a super-strong flying lizard thing. Anyway, at the end of the story HYDRA destroyed Yelena, and she died for a while. When she came back without explanation in Marvel Comics Presents a few years later, she didn’t have the Adaptoid powers anymore. I’ve always felt that the Adaptoid Yelena was probably a skrull.1 However, the Adaptoid stuff was mentioned in her most recent appearances in Spencer’s Secret Avengers, so??? You’re basically free to choose your own adventure with Yelena, since that’s what Marvel has done.
TL:DR; I don’t think Yelena has the chemical that keeps Natasha young, but who knows. She might have Super-Adaptoid powers, but who knows.
Panels from Black Widow: Homecoming #4 and New Avengers Annual #1.
1. This sounds like a joke, but it’s not. The rogue SHIELD cell and HYDRA powerbrokers were part of Bendis’s slow build to skrulls everywhere. A skrull infiltrator would be more interested in joining SHIELD than actual Yelena, and Yelena became not dead with no explanation right after Secret Invasion. But this is Marvel Comics, where the perfect continuity can never be.