Well, of course she can have seizures when your body is so immuned to a drug and then going off of the med.
Yes it could be possible the levels were a bit low at the time too.

Remember taking Dilantin for a length of time, can cause bone loss.

*Long-term side effects
Some other side effects only appear after a person has been using

Dilantin for a number of months or years. They are usually related to taking high doses. The most common ones affect appearance:

overgrowth of the gums
excessive hair on the face or body
acne
coarseness of facial features
Overgrowth of the gums (gingival hyperplasia) is more common in children than in adults. It can be reduced by vigorous brushing, daily flossing, and regular visits to the dentist, who may recommend additional treatments. If Dilantin is stopped, the gum problems won't get worse, and in some cases will go away within a few months.

Long-term use of Dilantin also has been found to cause weakening of the bones. Bone disease is even more likely if a combination of seizure medicines is used. People taking Dilantin should exercise, take vitamin D supplements, and eat foods rich in calcium. Some non-food sources of calcium, such as Tums and Os-Cal, reduce absorption of Dilantin. They can be used but should not be taken within about 2 hours after taking the Dilantin.

Some people who take Dilantin for several years may have damage to the nerves in their legs. Faulty reflexes can be seen in a minority of this group.

Damage to the part of the brain called the cerebellum may affect others who take Dilantin for a long time, especially if they take high doses. Damage severe enough to produce significant problems is uncommon, however.*

best of luck to you
Lisa
http://health.groups.yahoo.com/group/epilepsyapproach/