Absolutely, start out small. What if it turns out that your Mom decides that she doesn't like raising chickens?
Here's something to consider...a hen's production is best until her first molt, then it drops each year thereafter. If the goal is to raise layers in order to sell eggs, something needs to be done with the hens whose production isn't paying for their upkeep. Will your mom be able to process, or find somebody that can do it? I have a friend that raises hundreds of chickens on pasture, both layers and meat birds, for the Farmers Market. He and his team can process the nonproductive layers into "stewing hens".
Ditto on checking to see if there are restrictions on the maximum # of chickens you can keep.
If her goal is to supply eggs for personal use, maybe sell extras and the chickens are to be "pets with benefits", get a few chickens this year and add a few more later on to offset the drop in egg production.