I'm switching frames and parts with a friend and she wants to keep her crankset, and i want to keep mine, but shes using a Miche Primato Track (107 mm) square tapered bottom bracket and I'm using a sealed cartridge truvativ 108mm PowerSpline. We noticed the 1 mm difference. Can her bottom bracket fit into my frame? and likewise mine into hers?

thanks

PowerSpline won't fit into a square taper and vice-versa.
You guys need to exchange bottom brackets as well and yes, your bottom bracket will fit into hers and likewise, hers to yours.

do you know if the bottom bracket shell size matters?

yes. most modern frames are English treaded. But somtimes you can encounter Italian and even French threading. English is 68mm

Should be able to as long as both frames and both bottom brackets are all 68mm english threading. The sizes you have listed are widths and do not make a difference.

Yes, switch away.