I admire Elinor so much. She is a kind of person who is not reticent to the point that she does not portray any feelings when circumstances calls for feeling. She is only reserve when one needs to be reserved.

"and her feelings were strong: but she knew how to govern them."

She is an example of a flexible character. She is considerate to her mother's and sister's feelings. She acts properly for manners require it. Maybe if she taught Marianne how to govern one's emotions and feeling, Marianne wouldn't have been what she is as the story progresses (but then Margaret might be a pupil).

As of now, we cannot fully examine every corner of Elinor's character but in just the one paragraph of description and her being her mother's counselor tells us what kind of person she is.