Maybe shes having great time but dont wana cheat on someone she likes more.
Or she might just ensure there are feelings in first place. Like shes getting attached to you from kissing and etc but not sure if you getting more attracted to her. Basicaly say you like/love her give her compliments make sure she knows.
And if by going down there you mean oral then compared to man half of the woman dont like oral.
However if you say shes shy as girl can be then ofcourse you will be the one innitating. To make her confident give lot of compliments and be confident yourself so she can get infected with your confidence. Also it works well when you say some shit about yourself, kinda bring yourself down so she feels upper. And with shy persons you want to take pressure off by making them feel free, like nothing is expected or pressured that theres always plan B. Dont always place all atttention on her but sometimes concetrate on other people while with her. Divide the attention cause shy girl wont feel comfortable being in centre of attention.
So basicaly talk good about her say some shit about yourself and put primary attention on non intimate activity and sometimes talk about or with other people. And be confident. Shy people like laud, outgoing, confident people.
Doubt kills more dreams than failure ever will