Wedding Dress Nightmare

My poor niece, has not had a good experience with her wedding dress. After trying on many dresses, she eventually decided on one of the first dresses that she tried on, with alterations that they agreed to the back of the dress, and this was ordered from a local shop in September last year.
In December a phone call was recieved to say that the dress had come in, and she could come and try it. At the same time as this there was a death in the family, so the actual fitting didnt happen until January.
The dress was ready for her when she arrived at the shop, but as it was being put on, she realized that it wasnt a new dress, but was the sample dress that she had tried on originally, complete with pin marks in the back and a new scorch mark at the front! When confronted the shop owner originally denied that it was the sample dress, but eventually stated that my nieces dress must have been given to a bride who had bought the sample dress. She was asked if she had ordered the dress in the first place, and was adament that she had, but was unwilling to provide any proof that she had placed this order.
She initially refused to refund the money, asking for a chance to put it right, this was agreed, but while sorting this out, she continually moaned about how she would be out of pocket, etc etc, at which point my niece said, forget it, I will go elsewhere!
Thanks go out at this point to Mrs P&P, for advice, and Madeliane Issac James for offers to help.
So, at this point we are in mid January, and the wedding is in May, ands we have no dress!
My niece tried on a few more dresses, but then ordered the same dress from a different shop. The only other stockist in the area, and was told that it wouldnt be in the shop until  May 16th (wedding is on the 29th), and would still need the alterations at the back. My sister attempted to contact the company to try and get it delivered earlier, but met with resistance, and was told that she couldnt speak with the manager. A few weeks later the manager contacted her and said that she couldnt believe that she hadnt been told about the situation and would ensure that the dress was delivered as soon as possible. One helpful person!
The dress was delivered at the end of April, but the shop stated that she couldnt have a fitting until after her hen weekend in case she put on weight! So last week was the fitting. On arrival we were pointed to the changing room, and left to get on with it. So I dressed the bride.  The dressmaker/seamstress attended and the changes were discussed and agreed. Yesterday we had another appt, and again were left to dress the bride. The changes to the dress had been done on a temporary basis, but werent right. We were discussing this when the shop assistant asked us to leave the changing room so a member of her family could try on a dress for her daughters wedding. A member of staff assisted us at first with trying to get the look right at the back of the dress, but then said 'you know what she wants, you do it' and left me and my sister on the floor pinning up the dress. The seamstress arrived, and played with it, and ended up with something that the bride thought was ok, but still not what she wanted.
The situation at the moment is that the seamstress has taken the dress to work on, but I know my neice isnt happy with it and its not the look that she wants. And its not her being a bridezilla.
The question now is, do we stop the seamstress, and look for someone else who hopefully get the idea of what she wants and get the look right? Or do we let the seamstress continue and she walks down the ailse in 8 days time in a dress that shes not totally happy with? We are at a loss as to what to advise her to do. The whole thing hasnt been a pleasant experience for her at all. Such a shame :(