E.C.
From what I remember (I have twin girls who are now 6 years old), babies one year and younger can get ALL their nutritional needs met by breastmilk or formula (both of which are more calorically dense than solid foods) so more "meals" could actually be *decreasing* the amount of calories they get per day
perhaps your daughter can consult a pediatric nutritionist? Sometimes pediatricians can be a bit overeager to push solid foods as the "cure all' for young babies' nutritional needs when that might not be the case. Also, nutritionist Ellyn Satter's book "Child of Mine, Feeding with Love and Good Sense" is a good practical resource about child nutrition
And if your daughter's not already connected with a parents of multiples club, I highly recommend checking it out - great place to connect with other new parents as well as with "been there/done that" parents who can provide encouragement and info on what sorts of things they found helpful in caring for two (or more) babies at once.
http://www.NOMOTC.org can help you find the club nearest you (they have a "zip code locator" that will direct you to the clubs in your area). The parents of multiples club for the Oakland/Berkeley East Bay area is Twins by the Bay http://www.twinsbythebay.org