She shouldn't be eating straw...she was probably just chewing on it and maybe got too much in her mouth? If she's actually hungry, then her mother doesn't have as much milk as she should for some reason, whether that's genetic, nutrition, or whatever. If the calf is old enough to start eating, say 3 or 4 weeks old, you might try a creep feeder to start the calves on feed. I'd rather have her chewing on something that's gonna do her some good than straw.
Calves are very curious. And who knows what makes some animals do things they might do. That may or may not be something you should continue to watch for. It kinda seems though it's always the same ones that get into stuff like that. Just like kids, I reckon...
