I have not seen the movie personally. So I can not comment on that.
As far as that site goes, if that’s the way it really happened. The Church did right to say no the first time.
My son was diagnosed with Unexplained Epilepsy in May so I have learned a thing or two about this.
First off the goal of those with Epilepsy is the same goal that those with Asthma and Diabetes have. CONTROL! Everyone of us has a seizure threshold. For most people that threshold never gets crossed. For those with Epilepsy it does. The reasons may be known and in a lot cases (such as in the case of my son) they are not known.
There are many different types of seizures. The site never says which type she had. Many people that do have seizures experience an aura, which can be a strange sound, sight, smell, or a physical sensation. This is basically a warning for them. I’m sure that her doctors would have thought the faces she was seeing were nothing more than an aura.
Anticonvulsant drugs are extremely powerful. Your talking milliliters here, not tablespoons or teaspoons. My son was started on 1/2 ml and in less than an hour he was extremely loopy. Fortunately they adjust quickly to this so it doesn’t last long. When people are started on these drugs you are worked up to your regular dose. You do not just jump into it. The older anticonvulsant drugs have a reputation of having bad side effects. Some include damage to the liver. People on those drugs have to under go testing every 3 months for liver damage. Another side effect is also depression. One of the newer drugs Kepra does not have all of the side effects that the older drugs have. So improvement is being made.

The one side effect that our doctor told us about Kepra is that if they have a negative reaction to it they will have a really bad personality change. He said it is like night and day. Fortunately we never experienced that. However, for several weeks we did have serious disciplinary issues with our son, he’s 3 1/2 yrs old. After several weeks he settled down and is now basically back to normal.
When it comes to these drugs you can not stop cold turkey. You must be weaned off of them. Stopping cold turkey can have some bad side effects, including bringing on seizures. The site doesn’t say if this is what Anneliese did.
I do find it interesting that the site says this:
According to Physicians Desk Reference, taking Tegretol may cause epileptic obnubilation, (a lowered level of consciousness with loss of ability to respond properly to external stimuli) with fever and hypoxemia (lack of oxygen in blood). Anneliese had all these symptoms, which gave rise to the theory that the cause of death was suffocation.
The autopsy report, however, said that her death was caused by the malnutrition and dehydration that resulted from almost a year of semi-starvation during the rites.
When a person experiences a seizure their brain is practically running a marathon. One of the things that happens is they start losing oxygen. When my son was in the hospital back in May he had 2 seizures. During the seizures his oxygen dropped into the 80s. I’m talking with in seconds of the seizure starting it went from 99 to in the 80s! It is a rapid change. His average the rest of the time was 99.
Having watched my son go this I can definitely sympathize with her parents.

I’m no expert so I have no idea if she was really possessed or not. This is just what I know and I would say that it is possible that she was not possessed. However, I’ll leave that to the experts to decide that definitely.