I need to know if the following sentences are possible. Thank you very much!

1) Lake Titaca is situated (lies) between Bolivia and Peru and is the highest large lake in the world.
Can I replace "highest large" with "largest"? What is the difference?
2)Chile is situated on the west coast of South America. It borders Peru and Bolivia to (?) the north. It has got the driest desert in the world, the Atacama Desert.
3)When she was born, the doctors noticed that she had a problem with her feet. She was operated on her feet (?)/(She underwent an operation) and the doctors amputated her feet and part of her legs.
4) She didn't want to sit in (?) a wheelchair for the rest of her life. 5) When she was in her teens, she went to the Atlanta Paralympic Games and won three matches. She also starred in a fashion show for a famous clothes designer.
6) They diagnosed him cancer and told him that his chance of recovering was less than 50%. His dad is in a wheelchair. His room is always in a big mess (I need a synonym).
7) He enrolled at Dalesway Secondary when he was eleven. He had a talent for acting (or he had a natural gift for acting).He entered university when he was eighteen.

1) Lake Titicaca is situated between Bolivia and Peru and is the highest large lake in the world.

Can I replace "highest large" with "largest"? What is the difference?
http://en.wikipedia.org/wiki/Lake_Titicaca In the first paragraph here, it explains that "highest" refers to altitude (how high above sea level) the lake is, but "large" refers to the surface area of the water. Both terms need to be there. Also, watch the spelling of the lake.

2)Chile is situated on the west coast of South America. It borders Peru and Bolivia to the north. It has the driest desert in the world, the Atacama Desert.

3)When she was born, the doctors noticed that she had a problem with her feet. She underwent an operation, during which the doctors amputated her feet and parts of her legs.

4) She didn't want to sit in a wheelchair for the rest of her life.

5) When she was in her teens, she went to the Atlanta Paralympic Games and won three ___ matches. She also starred in a fashion show for a famous clothes designer. (What kind of matches? Tennis? Racquetball? What?)

6) They diagnosed him with cancer and told him that his chance of recovering was less than 50%. His dad is in a wheelchair. His room is always in terrible disarray.

7) He enrolled at Dalesway Secondary when he was eleven. He had a talent for acting. He entered university when he was eighteen.

I made other changes in your sentences. Be sure to read and compare carefully with your original sentences at the top of this webpage.