I appreciate the struggles of your grandmother, but I don't think your making a reasonable comparison.
First off, your grandmother would quality for public housing and/or longterm care. Which is not inexpensive.
Second, I've never heard of a combined CPP/OAS/GIS payment that low for qualified recipients.
As a rule GIS rises to ensure a minimum payment equal to the lowest possible CPP payment, plus OAS. (the minimum payment for someone w/no CPP income who is otherwise qualified is $1,487 per month)
https://open.canada.ca/data/en/dataset/dfa4daf1-669e-4514-82cd-982f27707ed0
OAS/GIS generally requires you be a resident of Canada for at least 10 years after the age of 18 for a partial payment (40 for a full payment) . But even if grandma didn't qualify initially, she would become qualified after a period of years. (as I understand it)
If you argue that retirement incomes writ large are inadequate I'd be fully supportive. I also support raising the retirement age to 68 which would fully finance a major increase in benefits.
If you want to argue that someone who has been in Canada less than 10 years should receive full retirement benefits.......I'm open minded and progressive but that might be a struggle. Perhaps partial payments should be higher.
Regardless, I fail to understand why you are upset that someone you care for is not receiving the kind of support you feel she needs, but you would gladly deny proper support to someone else.