We had our daughter repeat 4th grade... and for her, it was the BEST thing we could do.
However, that was the right time for us... she was struggling, and needed a year to catch up. We also moved several states away that summer, so her friends at her new school and community didn't need to know.
Her second grade teacher suggested it, but we didn't feel that was the right time. (We also went back and talked with her previous teachers, and they agreed with us, that it wouldn't really help at that point.)
I know you are struggling with this decision.... but do you really want your child to continue to struggle? She is young...... school just gets harder, not easier...... if she is struggling now, think what it may be like in future years. You don't want to destroy her love of learning and desire, if she continues to struggle. Why frustrate her?
My daughter is very bright...... and just finished her Doctorate in Microbiology at Johns Hopkins School of Public Health, and just started working for NASA ......