On a safe note, get a restraining order on him after speaking to him about the issue and if he chooses to continue pestering her. But i ask, is he by any way harming her? Does she feel distressed by him? Or has he indicated he is taking advantage of her disability? All things that need to be considered before working energy within the situation.
You can work some energy yourself to protect your daughter, if she is not able to do it herself you will need to because she is a part of you, your connection will be stronger than that of someone else.
You will need nothing for this, just a clear mind and focus. You can try this in two ways, both in which you will need to be in a calm place for both of you, somewhere at home is good if possible.
The first method is placing your palm on her chest just below her neck in the center. Close your eyes and have her to relax as much as possible and envision a ball of light at the end of your palm. In your mind, make it bigger while asking it for protection and warding from those who wish harm on the person you are touching. If you have a deity or an Angel or Guardian, ask for their assistance also. Make the ball of light in your mind big enough to encase her whole body. Keep it that size in your mind for about half a minute asking for protection, saying that "this is from me to you" before your lift your hand away.
Secondly you can try warding an area, in much the same way you create the shield around your daughter. But instead put your palm to your own chest and create the ball of light from within you and spread it as far out as needed to ward the room or house. But dont make it too big or it will have no effect. You cant shut someone out from the world, they have a place in it, but you just want them removed from yours.
Also dont allow any negative or hurtful thoughts to influence these. You should not wish harm on this person unless hes harmed your daughter already (in which case i hope not) but you need to keep this positive because adding negative energy only ever does more harm and less good, for everyone.
Alternatively, if he is seeking her for romantic interest, there is a spell that you can cast which I have found to work in the past. If this is the case, let me know and ill write it up for you.