In The Secret Life of Bees, what is the metaphor Lily uses at the end of pg 132?What does she mean?

I think this metaphor is also meant to evoke the Black
Mary, which we learn about in Chapter 4 of The Secret Life of Bees,
in the same scene in which Lily and Rosaleen first meet May. Black Mary is a figure that
is "black as she could be" (70). She has "a faded red heart painted on her breast" (70)
and "a candle inside a tall red glass threw glints and glimmers across her body" (70).
The statue's impact upon Lily is profound, "so big it ached like a moon had entered my
chest and filled it up" (70).  May, of course, is black, as well, with "palms pink like
the bottoms of her feet" (71), which fills Lily with "tenderness"
(71). 

Black Mary and May, with their contrasting blacks
and shades of red, have a strong and positive impact upon Lily, the Black Mary seeming
to confer some serenity and protection upon her, and May making her feel very
protective.  I do not think the metaphor later on in the book is a coincidence at all. 
We are meant to remember that Black Mary's heart is on her outside, providing strength
and hope, while May's heart, on her inside, makes her
vulnerable.