She over analyzes situations because she's scared of what will happen if she's not prepared for it.
She over thinks everything because she's afraid of what will surprise her if she doesn't expect the worst.
She over exaggerates feelings because she's frightened of what she'll feel when she gets her heart broken.
She's over protective of you because she's horrified of what she'll lose if you start liking another girl.
She overreacts to little things because she's terrified of how much it matters to her.
Sometimes, it may seem she goes overboard on a lot of things, but it's all out of fear of loving you too much.