Child's Relationship With Twin Siblings
Very often there is tension among three siblings. It seems that one is always left out when the other two gang up or even when they just play together. When two of the three are twins, the alignment has probably almost always been the twins against their sister.
Because she is older, your daughter went through the common experience of older children—being displaced and not being the middle of the universe any more. In this case, though, she was outnumbered at the same time when the two boys arrived. So she may feel that she has had to work especially hard to get her share of family resources ever since then. Finally, the fact that the twins are boys and the other sibling is a girl also can create distance.
One thing that you as parents can do is to try to encourage your daughter to help to support the boys. She could help them with homework and explain things they don't understand. She also could help to "mentor" them at school or out in the world.
If there are two parents, a mother and a father, it may be helpful if Dad sometimes does special things with the boys and mom does things with the girl. Actually, each of the children should have some time alone with each of the parents. That helps to build all of the bonds in the family's relationships and helps each child feel special and understood. It also could be fun to do things with your daughter and one of the twins together. Let them get to know each other when the twins are separated.
The twin relationship creates some unique sibling needs. You should make sure the twins are allowed to be individuals and do things alone. Don't always call them "the twins." Use their names, and let them be separate. If your daughter feels that the boys are always a unified front, she may feel threatened. It may be easier for her to feel that she can deal with them if they are treated as two individuals.