Much of the technical issues with AI bodies is dealt with by hand waving and lampshading. Some details have been addressed more or less directly, however.
Bubbles has a
liquid coolant. We also know
her body is warm to the touch. Her skin's ability to radiate heat may be sufficient to keep her cool in most circumstances. Adding a system that simulates respiration may also facilitate heat exchange with the environment while also making her seem more human. She may also have sufficient heat sinking ability to store heat until she enters her sleep cycle to recharge and dissipate stored heat.
They may not have made those systems redundant. Her armor was designed to withstand anti-tank weaponry. It may have been assumed that if something hit her hard enough to damage internal systems, she was going to be down for the count anyway.
We generally do not inquire about anybody's
"bits". They are hers to worry about and hers alone. Curiosity is natural and normal, but it won't be addressed.
Skin is useful stuff. Feeling is useful, too. It helps a lot in making assessments about an object's texture, rigidity, and temperature, detecting contact with objects, etc...
She could have been anything! Given that she has indicated that she was not
always in the military prior to meeting her, she could have had a different body prior to service. She could have been in whatever state AI are in when they initially form (which hasn't been addressed to my knowledge). Her initial military service may have had her in a tank or MRAP or a fighter jet. May would be super jealous. We may never know.
*edit*
Wow. Almost 40 minutes between IICIH's post and mine and I started before there were any replies. I must take a long time to formulate my responses.