Smidge has a steel bladder - any advice?

New girl has only peed about once every 12 hours so far.  It's bizarre, I've never seen a dog hold it so long!  And she doesn't go pee and poop at once either, it's like 12 hours between each, at separate times.  So last night she finally peed, and this morning she pooped, but did not pee.  I left for work and she still hadn't gone.  How can she be asleep all night and not have to go in the morning??  She's not peeing in her crate, either, I've checked.
 
I'm going home at lunch to let her out, but it will have been 12 hours again between pees.  She doesn't eat much, but she does eat and has been drinking normally.  I'm just flummoxed by this.  How do you housebreak a dog that won't go?