Thank you for your question. Although each circumstance is different, a starting point, after making sure you and your spouse are on the same page, may be to have a clear conversation with your inlaws to find out why they are uncomfortable with your daughter wearing hijab. The second step would then be to make absolutely clear that this is something you would like for your child and that you are not happy with any type of discouraging. In short, it is important to set a clear boundaries and if that boundary is not respected then you can think of the next appropriate action.
May you always be successful