I don't know what I would do if I were trapped on the roof of a burning building. Unless I could be certain of surviving a jump, I might just want to hold on to what time I had on the roof, instead of giving it all up in one jump (obviously, this depends on the height of the building, and the condition of the ground below).
In this instance, it seems that a jump from the roof, without a bamboo pole to slide down (which burned up after Alistair and the children slid down), would mean instant death.
[Amy] looked down. Far below was the construction debris. Twisted coils
of wire, concrete, nails, tangles of rusty rebar. There was no clear
place to land. Even if they could survive the jump, they could be
impaled on the sharp objects.
The 39 Clues, The Clue Hunt: In Too Deep page 195 (chapter 25)
Also, at that point, Irina had already given up on her own life, having accomplished her goal of saving Amy and Dan.
From high above, Irina watched them. The roof was so hot now it was
agony to stand on it. The smoke rolled across her and cleared. She
felt so far away from them. How hopeful they were. They didn't know
yet that it was too late. [...] She had only seconds. That was all
right. She'd saved him. She'd saved her beloved boy. No, not Nikolai.
Dan. Dan and Amy.
To be fair, after that point she does seem to reconsider giving up her life "Was she really ready to let go of life?," but it appears that by the very end she decides that " it was worth it to me," and hopes that the children realize that. (Anyway, those thoughts were in the very final seconds of Irina's life before the building collapses, and it was too late to do anything else at that point.)
Additionally, it appears that it was a point of pride to Irina to remain standing as long as possible, which would not be possible after jumping and breaking bones/getting impaled.
It was a great effort to keep standing. She would keep standing. She
would die a better person than she'd lived. That wasn't too bad, for
an ex-KGB spy, not to mention a Cahill.