Second Home/Rental Property — property tax deductions

[Xavier Paredes]

I'm helping my mother figure these things out. Sorry for any rookie questions.

She owns 2 houses. House #1 where she lives, and house #2 which she rents to my sister.  

I've read that your primary home's property taxes are deductible. So that seems to be clear.

However, I'm not sure if property taxes are deductible for house #2. Are they? 

In case any of the following matters at all: 

1. My sister's been renting house #2 for several years but this question has just come up recently because I wasn't involved—until now.

2. My mother has been retired for some years now.

3. My mother doesn't have a formal landlord-tenant contract with my sister (she does pay rent on time though).

Again, sorry for any dumb question.

TIA!