Are they close family and friends or just random facebook friends she doesn't really know?
I come from a very large, close family were we number over 50 people (just my aunts, uncles and cousins on my mom's side). When they throw a shower (not all 50 come since it's usually just the females but other extended members and friends come too) the host has a few other's help out and do a pot luck of their own.
The guests do not bring the food but maybe 5 aunts will supply the needed food, this allows them all to help out, take on a smaller part of the work and cost. But the guest just see a well laid out assortment of foods.
Is your family big enough to have a few others help with food?
If not can you tell her it is too much and ask her to have 2 showers and have someone else host the other half, you take on the family and friends you know and the other party can be hte co-workers or random people she may have invited?