I think I finally noticed the Kraang symbol on Irma. It's her hexagonal bracelets. The Kraang use hexagons as their symbol. A single hexagon may be like an individual cell of a hive. Seven hexagons together (like the TCRI logo) may represent the hive itself. If this was meant to be a foreshadowing sign of her Kraang involvement, then we should find out how early she's been wearing those bracelets.
Now let's see... Irma's earliest appearance was in Season 1 Episode 11 Mousers Attack!, but only as a caller ID on April's phone. Her first appearance in person was in Season 2 Episode 4 Mutagen Man Unleashed. ...and yes, she's wearing the hexagonal bracelet on her right wrist. It may mean she's been Kraang in all of her appearances in-person. Of course, April has known her for longer than this, so I suppose it's possible Irma may or may not have been a real human in the first season, but was swapped out with Kraang Subprime during the second season.
However, there's also April's realization in The Invasion, Part 1 that her best friend of the past year had been Kraang. Since the combined durations of seasons 1 and 2 took place in-story over the space of less than a year (the turtles turn 15 in Season 1 Episode 1 Rise of the Turtles, Part 1, and are still 15 in Season 3 Episode 4 The Croaking), Irma may have been Kraang since even before the pilot episode. We just don't know enough about the early Irma, since she only became a supporting character since season 2.
But I think, if the hexagonal bracelets are a sign of her being Kraang, then it would be relatively safe to assume that she was Kraang Subprime in all of her in-person appearances—every single one. Damn. I still want them to meet human Irma.
But there's still another piece of evidence that complicates the equation. That being, Irmabots were mass-produced, just like the Normans and the Mrs. Campbells. The question is, were these mass-produced models based on original human templates? Or were they original designs by the Kraang? If there was an original human Irma, there might also be an original human Norman and an original human Mrs. Campbell. Hell, they might have all three of them (and perhaps other human templates) imprisoned or frozen somewhere. Season 2 Episode 9 The Kraang Conspiracy had mass-produced Aprils, but those were biological duplicates rather than robots; however, it does establish that the Kraang have used human templates to mass-produce facsimiles.
Alas, this is all speculation.