MianMian is a child who hates giving her mother a lot of work; so that makes their relantionship in Step 1 close but rather distant, as she doesn't like to tell when she is not well, she LOVES her mother and she couldn't ask for a better mom than Opal, It's just that Opal works so much that MianMian feels alone sometimes, before moving into Golden Grove, she couldn't make any friends because she has some trouble to express herself, so most of the time, MianMian don't talk much.
It gets better when they move to Golden Grove, MianMian learns that she can tell what makes her feel bad without feeling guilt of hurting others feelings, so that makes it a little better, but It's hard breaking old habbits.
In Step 2, Opal and her ARE really close, MianMian now trusts her entirely, sure, her mom still works a Lot, but MianMian is very busy with school and being a teenager is though, It's so much changes and her friends start growing apart; so in Step 2, Opal is who she knows she will come home to, her safe spot, wich makes her feel more open towards her Mother, and feel more useful since now she can help her mom with more chores.
MianMian feels more at easy with familiarity, so they have a really strong bond at Step 3 and it doesn't changes even on Step 4!!