Are you in the United States?
If so, then I definitely think you should give TAPS a call. TAPS is the Atlantic Paranormal Society, and they help out families like yours. Helping children is their number one priority, especially when the children are too scared to go about their daily lives.
While you're waiting on a reply, I encourage you to check out a few things concerning your house and the area around your house.
1- with children, there is always a chance of poltergeist activity. They can be the focal point of the activity, and even cause it. You can do some background checking to find out if this could be happening to your daughter. Poltergeist activity occurs where there are rich limestone deposits. Check out the geology of your area for limestone deposits. You may be able to find this through the USGS, a local park, a library, or a university.
2- Check your home's electrical wiring. Are there any wires that are exposed and not properly shielded? This can cause high electromagnetic frequencies that can cause bouts of depression, paranoia, the feeling of being watched, and hallucinations with exposure. Check the spot where the girl constantly feels a presence behind her. Is it near any outlets? Are there wires running overhead?
3- The Earth gives off certain magnetic fields due to its rotation and revolution. In these fields, very weird things can occur, at least I think so. This can be discovered through the equipment that TAPS uses though.
Definitely send an email to TAPS. One of my relatives did as the ghosts were affecting her 2 yr old and newborn, and they sent a local team out to investigate.
Do not contact psychics or mediums. Priests believe that these psychics can stir up the ghosts with their presence and make the situation worse for you when they leave.
If your daughter has a ouija board, now is the time to remove it from her room. Store it, don't destroy it. If her friends and her have been using it, you need to know! The ouija board can attract demons through it. Demons are spirits that never existed as a human before. If you throw away or destroy a ouija board, you may find your troubles worse than before. So, keep it until a professional tells you its safe to get rid of.
There are three types of hauntings. The first is a residual haunt, where the energy of a certain moment is taped and forced to play over and over again in a certain location on Earth. Residual hauntings do not interact with people, they just let their tragic story unfold. They are not spirits left in this world, just a memory that time has saved. It does not sound like this is what you have.
The next type is an intelligent hauting. These were human once, they are now spirits and can interact with you. Sometimes they pick up objects, brush against a person, etc. They usually do not mean harm. This is most often the case when there are hauntings.
The last, well I won't scare you.
Please, contact TAPS asap for your daughter as they can collect evidence, and they will disprove or prove that you have ghosts. At the end, you may feel more at ease.