H2B niece as bridesmaid

Traditionally, the bride gets to choose her bridesmaids and attendants, but in practice, I know very few brides who haven't had to deal with someone else telling them who they should choose!

I guess it depends how much you don't want her as bridesmaid v how much emotional fallout there will be with the groom's family if she isn't. All I can suggest is that you explain that you don't want a big wedding party and that if you have your OH's niece, close friends will be offended if you don't also ask their children. After all, it doesn't sound as if your parents have caused problems because they didn't get to pick the groomsmen!

If it would help and you are happy to compromise, you could follow up your explanation by suggesting your OH's niece carry out some practical role at the wedding - maybe being in charge of handing out orders of service like an usher - since she is your OHs relative and he is the one who wants her included, it would make more sense for her to be in the groom's party anyway.

Where’s the harm in letting her be a bridesmaid? Think about your husband to be and the girl herself. I think we get so caught up thinking about ourselves during our wedding plans that we sometimes forget to consider others and their feelings.

As per traditional rule @RomainticGreenStationery27135 has already mentioned.

but its life, sometime we have to compromise. We can not follow the rules everywhere specially with our loved ones. I would recommend compromising if possible for you.