'y' to replace [à+ thing / object / location]

Question

The lesson said that y replaces [à+ thing], and that an indirect pronoun replaces [à + person].

The question was "Il pense à sa famille. Elle....pense aussi." 'Famille' is people, so why is the answer given as 'y' and not 'leur'?

Maarten Kamp · Accepted Answer

John, 
In French, 
“la famille” is typically used and treated grammatically in French as a singular collective noun for ‘ the ensemble ‘ as opposed to ‘ individuals in the/an ensemble ‘. This distinction is stronger than in regular English usage. 
The adverbial pronoun “y” can replace prepositional phrases with “à” when they refer to things, places, or abstract concepts. 
For example it is the same principle in :
“Tu appartiens à cette équipe ? Oui, j’y appartiens.” 
Also, when it comes to a pronoun replacing ‘ people ‘, you couldn’t use ‘ leur ‘ here as ‘ penser à ‘ does not take an indirect object ( hence my specifying that ‘y’ is an adverbial pronoun, not an indirect object ). ‘Penser à’ will instead be followed by a stress pronoun, and you cannot replace this with an indirect object pronoun before the verb.
 “ Je pênse à mes parents, oui, je pense toujours à eux. “
See previous comments by Chris and Céline to a similar question on how to treat ‘ la famille ‘ grammatically, and to Laura Lawless for discussion of ‘ penser à ‘.
https://french.kwiziq.com/revision/grammar/how-some-plural-nouns-in-english-are-singular-in-french-and-vice-versa
 
https://www.larousse.fr/dictionnaires/francais/famille/32798
 
 https://www.lawlessfrench.com/grammar/verbs-with-a/