The tag that tells me the height weight specifications are under the seat in my car. I have to fold the seat up to look at it.
Do you have a user manual? It might be in there if the seats were factory fitted. My car has anchor points I think at the top of the back door. They're all over the roof & on the back of the middle row seats in my car.
To buy a seat, make sure you put it in, put her in it & put the seatbelt around it. So you know if it all fits right before you buy