Could consider a partial twist or defective digestive tract... When a calf drinks milk, there is a groove that is designed to send their milk directly to the abomasum, where it is digested and then sent on through the rest of the calf. An adult animal no longer has that capability, as all their food gets sent to the rumen where bacteria break it up and digest it. Were that groove not present or not working correctly in the calf, all their milk would be sent to the rumen (where fermentation of hay and grain normally takes place in an adult animal). Now picture a calf's milk sent to the rumen and the lactose being fermented... there's a cause of bloat. Could explain why she does better when just on electrolytes.