She is eating a noodle.
(Does this mean she is eating a piece of noodle? When she is eating "noodle' for breakfast, what expression do we have to use? 1. She is eating noodles. 2. She is eating a noodle.)
2 answers
if she's only eating one piece of a noodle, then it would be She is eating a noodle. If she is eating a bowl of noodles-- she has more than one piece of noodle on her spoon, fork, etc, then it would be She is eating noodles.
"anonymous" is correct. Use #2.