The 10x seems very unrealistic. But assuming that were the case, the taxes would be the least of your worries because things like supermarkets, electricity, phone, water, heating... would also go up heavily.
The more realistic picture is that grandma living alone in a rather large, old house, whose price, heating etc. went up quite drastically. That is already happening, in particular the heating part. Just have a look at Europe and the UK. The question then is, and I am not picking a side here, whether you spend public money so she can afford to stay in that large house or you make changes.
groceries may be a bit more expensive, but "phone, water, and heating" go up with a real estate boom? not in my experience. Price per kilowatt/water meter is the same if you're in the ghetto or "affluent" neighborhood.
Not unrealistic at all. After the fall of socialism, we had a law, where current tennats could buy apartments from the government for very very cheap.. we're talking about a mid-range new car prices back then (to avoid having to calculate inflation), and quite a few years after that the prices were very low. If we're talking the attractive parts of the city center, a one bedroom apartment can easily cost 500keur now. For comparison, even ~15-20 years ago, that would cost maybe 100keur (with some inflation until now), especially if it didn't have parking options nearby (but airbnb investors don't really care about that that much, they can rent a parking spot a few 100 meters away in a parking garage.
We had a law, that somehow got repelled by some lobbyist, where all the public money given to help was then taken out of inheritance (so the kids had to either pay it back, or property got sold at an auction, government took the money and the kids got the rest). This would solve the help-money issue.
The more realistic picture is that grandma living alone in a rather large, old house, whose price, heating etc. went up quite drastically. That is already happening, in particular the heating part. Just have a look at Europe and the UK. The question then is, and I am not picking a side here, whether you spend public money so she can afford to stay in that large house or you make changes.