Is Susie an unbiased narrator? Does she soften the impact of her mother's infidelity, etc.?

Yes, she does
understand more than a regular first person narrator would understand, but she is in no way
unbiased.  She tries to be understanding, and she generally is, but she does have an opinion on
who is doing what and how that effects everyone else.  For example, she sometimes sends
"prayers down to earth," in hoping for a...