Rasmussen's encephalitis is thought to be a viral related disease (although no specific virus is known), causing progressive malfunction of one hemisphere of the brain. There are usually frequent partial seizures, and loss of function of that side. Sometimes loss of fuction can be from seizures itself from whatever other cause, so you need to be careful about whether this might be a cause of the 'loss of function'.
IF Rasmussens indeed is the diagnosis, and this may need to be confirmed by a brain biopsy, although sometimes the clinical picture is diagnostic, then there are some treatments to slow the disease such as steroids and IV immunoglobulin, howevere results are mixed. The main effective treatment is surgery to remove and disconnect that side of the brain - a hemispherectomy. As it starts at such a young age, most patients can have a normal life with only mild to moderate disability, and can walk, talk fairly well. If less than this surgery is done, the likliehood that seizures will return is high, and if untreated the other side of the brain can become involved also (over years). The best opinoin to get is from a major pediatric epilepsy center like the Cleveland Clinic, to make sure what the diagnosis is, and assess for surgery if appropriate.
Good luck
I am no doctor but from what I know the sooner you remove the defective part of the brain the better the outcome. Here are some links which may be of some use to you, one is even from the Cleveland Clinc.
http://teacher.scholastic.com/researchtools/articlearchives/humanbody/lifewithhalfabrain.htm
http://www.neuro.wustl.edu/epilepsy/pediatric/articleHemispherectomy.html
http://www.clevelandclinic.org/neuroscience/treat/epilepsy/surgery/procedures/hemispherectomy.htm
Thanks for the links. I appreciate you taking the time to reply.
Paula