Read the poem. The Courage That My Mother Had

by Edna St. Vincent Millay.

The courage that my mother had
Went with her, and is with her still:
Rock from New England quarried;
Now granite in a granite hill.

The golden brooch my mother wore
She left behind for me to wear;
I have no thing I treasure more:
Yet, it is something I could spare.

Oh, if instead she’d left to me
The thing she took into the grave!—
That courage like a rock, which she
Has no more need of, and I have.

In "The Courage That My Mother Had," what does the phrase That courage like a rock tell readers about the speaker's mother?

She protects the speaker from harm.

Her personality is difficult to relate to.

She is strict and inflexible.

Her bravery and strength is unwavering.