That's not the case at all. She doesn't point and shout, "Wow you guys, there's my mom!!!," but she doesn't just pass by without taking note.Leia doesn't recognize Padmé? That doesn't gel with ROTJ that well, do it?
In the comic, Leia passes by what looks like a stained glass portrait of Padmé in her full Queen Amidala makeup from TPM, in the red gown from the start of the film. The portrait shows Padmé in profile, and Leia imagines that Padmé turns and looks at her, says something to the effect of "that woman..." and then shakes it off and moves on.
If anything, this helps reinforce what Leia says in ROTJ—all she has of her mother is images and feelings, and here she literally sees an image and gets a feeling. (Though if she knew what Padmé looked like without makeup, and then saw a stylized interpretation of her with the heavy makeup, I don't think anyone would fault her for not seeing the connection.) So it's possible that this sort of thing has happened to her before, or that she can sense some kind of connection between them, similar to how she "always" knew that Luke was her brother. That's how I explain the discrepancy between ROTS and ROTJ—Leia can sense familial connections better than Luke can.