Can she take in as many children as she wishes?

Certainly not! A limited number of spaces is one of the advantages of a home childcare professional. This gives parents a guarantee that their child will receive the proper amount of attention and care. The number of children allowed in the childcare provider's home is legally determined by the provincial government so it varies from one province to another. If there are multiple caregivers the number of children allowed is also increased.

So how many can she take?

Each province has different laws regarding the number of children a home childcare provider may care for in his or her home. Often there are limits to the number of infants vs. school-aged children, for example, in New Brunswick the maximum if all children are between ages 2-4 is four children and eight children if they are all school-aged. 

Note that the number of children allowed is also dependent on whether the childcare provider has registered her home as a home daycare facility. This is not mandatory if she cares for few children (the exact number varies by province).
In almost all provinces the childcare professional's own children, if she has any, are included in these maximum numbers. This website is a great resource for consulting the rules and regulations in your province.