I would recommend a couscous dish because it's a nice light starch which you can flavor with pine nuts, mushrooms or anything else that your mom might like. (see http://www.neareast.com/index.asp?bhcp=1
for some couscous recipe ideas). And most importantly, it's extremely easy and quick to cook so that you won't be overwhelmed with everything else you're making.
Another option could be light side salad... maybe something with mixed baby greens, pears, gorgonzola, spicy honeyed pecans and a citrus vinaigrette dressing. That would tie in well with the salmon dish.
A third option could be a carrot dish:
Not to Sweet Ginger Honey Glazed Baby Carrots
4 cups baby carrots
1 tablespoon ginger, grated
1 clove garlic, minced
1/4 cup honey
1 tablespoon butter
2 1/2 tablespoons water
1 1/2 teaspoons soy sauce
pepper, to taste
1. Combine all ingredients in pot.
2. Cover and simmer 7 to 10 minutes until carrots are tender, adding more water if necessary.