My initial belief was that it could, but after running a couple of tests I must tentatively conclude that it can't. At least, not directly.

It appears that, for the analysis, the clothing item must fit the character's unmorphed state. If the item's geometry is specifically designed to fit Irina's shape, rather than the default Stephanie, it'll remain offset from the default shape after conversion.

You can still do the conversion, but it becomes a two-stage process. Put the Irina clothing on Stephanie Petite and run your analysis as usual, then convert to Stephanie Petite with her Irina morphs set to -1. This should give you a clothing item that can be worn by regular Stephanie. You can then analyse and convert this new item as you would any other Stephanie clothing.