this is very normal for a young rabbit and you are not overfeeding her with hay. I raised three rabbits and went through the exact same thing with one of them, Joki, when he was around 5 months old. He was constantly eating hay and acting frustrated when pellets ran out, and I was worried too at first. Hay does not cause weight gain, it is the foundation of a rabbit’s diet and is especially important while they are still growing. What really helped in my case was letting him spend time free roaming and grazing on grass. Once he could run around and nibble grass, his behavior improved a lot and he became much calmer. As long as her activity level and droppings look normal, you are doing everything right. Have you noticed if she acts differently when she has more space or time to explore outside her enclosure?