This can be a bit of a catch 22 situation as epileptic seizures themselves can make you sleepy.
It can take a few weeks to adjust to the sleepiness, but my OH takes 1,500mg of Keppra (which I think is the maximum dose) and it does not make him unduly sleepy. I do realise that as he is almost certainly bigger than your mum it will have less of an affect on him than it would on your mum if she were taking that dose, but I would still give it a couple of weeks and see if she improves. If not, yes, go back to her doctor - especially if her eating doesnt improve.