BMW Questions? Ask a BMW Repair Expert for Answers.
The oil pressure decreasing as the engine reaches operating temperature is perfectly normal. As the oil heats and becomes thinner you will produce less pressure. No problem there.
The blue smoke is another matter. The most common causes would be worn valve guides or worn piston rings and or a damaged cylinder wall. I would say your best course of action would be to perform a leak down test. This will pressurize the cylinder and allow you to determine how much (if any) air is making its way pas the rings. That will eliminate or confirm the rings as the issue.
Unfortunately, you need a compressor and a leak down gauge set to perform the test. You might come out ahead by just taking her to a shop. You can also remove the plugs and inspect them for oil residue. At least that will tell you what cylinders are being affected and you'll sound much harder to take advantage of while visiting the BMW stealership :)