Nani - I am not sure about the skin color and tailbone problems, but sometimes after gall bladder surgery people end up with Sphincter of Oddi Dysfunction which I believe is what the Biliary Dyskinesia is - it's basically a muscle that attaches to the pancreas from the small intestines that is not functioning properly and is causing a back up of bile in the common bile duct.
Do some searching online for SOD (Sphincter of Oddi Dysfunction) and you'll get a lot of information. She can have a blood test to see if her liver and/or pancreas enzymes are elevated and that can be a determining factor of SOD, but there are three types of SOD and two of the three have elevated enzymes, Type III does not.
Good luck with everything - if it ends up being SOD, you'll want to find a hospital with a GI group that specializes in SOD and diseases of the pancreas.
Please, keep us posted!
One more thing about ERCP - it is nothing to look at lightly, it can be risky and if not done by experienced docs, there is a great risk of getting pancreatitis (there is still a risk even with experienced docs.)
An MRCP is much like an MRI and is harmless, but an ERCP can be risky. ERCP can be helpful if the doc can do manometry with it which measures the pressures of the Sphinter of Oddi when it contracts. If the pressure is high, they will perform a sphincterotomy which is where they will cut the SO muscle to try to alleviate the pressure, however this is not always a cure - it comes with risk so please be careful!
Here is a link to information about SOD: http://hopkins-gi.nts.jhu.edu/pages/latin/templates/index.cfm?pg=disease1&organ=3&disease=12&lang_id=1
However, if her skin color has changed, please call her doc NOW.