Only way to tell is when you dismount, the tire wouldn’t be able to tell any other way.

That has not happened in 100 feet. It most of been partially deflated last time it was used.

Retired tire guy here.

It needs to be replaced. The 100 feet probably didn’t do the damage. It was most likely the 1/4 mile it was low before it was parked.

That groove in the sidewall is worse on the inside.

Lucky for her, since it’s a Subaru, she’ll probably need all 4 replaced due to the symmetrical AWD.

Tire’s done once it’s been driven on. Once they take it off the rim, it’ll be full of rubber dust it ground off. You have to do at least two tires on an AWD car, but really all four if your best two aren’t great.

It’s probably fine. Speaking from 20 years of experience doing car repair and tire services.

But, the only way to know that would be to have a tire inspection done on the inside of the tire. The kind of damage that would be caused by driving it flat would not be evident on the exterior.

The tyre tread is low and with such a damage on the side wall I would recommend replacement – both tyres on one axle should be equal. So your Mum needs a present for Mother’s Day! Two new tyres!

Had a brand-new tire installed and the valve leaked. Light came on and pulled straight over. The tire looked fine, but a few weeks later it blew a hole in the side wall. The rim rubbing on the inside of the sidewall had almost completely shredded the inner tire. Could not tell from outside at all. I would have it pulled off and checked to see if it’s damaged before fixing or replacing.

Ex tire tech here, the tires are cooked, literally. That wear ring you see in the sidewalk is a “heat” ring. The tire rubbed against itself while flat and wore away the material/ overheated what remains. It is very likely to blow out if used at proper pressure again. The inside of the tire will have what I used to call “goth confetti” which is the sidewall material rubbed off.