You need to talk this out with your husband.
You also have the option to invite extended family to your home, when your daughter is present, for family occasions.
You also have the option to plan days out or your youngest children's birthdays to include extended family and your eldest daughter, if you can't for some reason host family events at your home.
Instead of being offended - you need to work out how to get your in-laws to spend time with eldest daughter and get to know her.
Because if they get to know her, they will probably bond with her. But only if you organise family active events - like picnics, parks, games in parks, halloween, Easter egg hunting, making cup cakes, going to a National Trust park or museum or petting zoo.
And if there are cousins of a similar age to eldest daughter, you should invite them to yours at weekends, so they develop a friendship.
And if your eldest is the only 10 year old, and there are no other children of her age group in the family, then that is absolutely why she is not included. They expect the youngest two children to play together ...
But who is going to be supervising/entertaining the solo 10 year old, who has no aunties, uncles or grandparents at all the events? Is that why you didn't notice for so long, because it was convenient not to make extra effort for entertaining/supervising dd?
DD can't force in-laws to take an interest in her. Only mum can do all that behind-the-scenes organisation to make sure daughter is included and interacting with in-laws. But mum also needs dad on board.