Why would you hate to get her the help that she needs? Nobody wants their child to have any problem, but there is nothing with any time limit for having a brain based emotional issue that requires professional intervention. Not being able to handle your whole world crashing around her while you fight with your husband and she deals with the new baby brother is not a character defect! I would suggest that you call a board certified child psychiatrist and get her some help, they will probably refer her for some play therapy, and if it is bad enough, she may need medical intervention. Depression, even when caused by events in our lives, is a very real medical issue.
When people feel bad, or feel extreem emotional trauma, it actually changes the brain chemestry which can cause depression and anxiety which are biological processess that are real medical issues. Address her emotional and psychological issues now, and don't heap on more by holding her back, this will do little more than to cause her to feel frustrated, feel stupid, become yet more depressed, and perhaps lose one full year of instruction such htat she is more at risk for academic failure. Children who are a year above age-grade are at high risk for full reading faliure, dropping out, drug use, and contact with the juvinile justice system once they get to high school. You have to look at how holding her back will effect her life, it is not a pretty picture and the data is very clear (although many people with kids who have been held back will give you glowing anecdote about this, the data is striking, next to socioeconomic status, being older than age-grade is the second most corelated variable to all the things I listed.)
Please put aside your fear of social stygma. She has an issue, get her help, just like you would for her urianry tract or pulmunary system. Insert the word "pee" for the condition you fear she needs help with, and see if you would feel the same. She can no more fix the chemicals in her brain that are making her feel bad than she can fix how her unrinary tract makes pee if it does not do so very well.
Flesh and blood. No shame. Get help. NAMI can help you get over your fears too, give the local chapter a call.
M.