Chancey asked why you would want to get the procedure done so I wanted to add that for us (both myself and my FD's birth mom are Hispanic) it is very much a cultural thing. Birth mom asked me if I would pierce the baby's ears and since if this had been my own birth child I would not even think twice about it, I talked with our CW and took birth mom with us during a visit to have them pierced. FD was was 4 months old. Yes, it is cosmetic but for many Hispanics it's just how we do things. :)
Yes, I married into a Hispanic family, so I know the culture in regards to ear piercing. The issue here is the mom is NOT asking for it, the foster mom is. If the mom was asking for it, it wouldn't be an issue for me. Why can't the fosters parents just wait until this child is in their forever home before doing this? Why does the foster mom feel like she has to have a child ear's pierced when that child is not hers yet. AND, just because she may have beliefs on ear piercing does not mean that she should have it done to a child that is not hers.
Your argument that this might be a culture identity thing is similar to saying an AA child's hair needs to be straightened if they are staying with a anglo family - wrong on all counts.