These are the very last sentences. I'm unsure whether to use she or her (in sentence 6). Do you say "found out" or found/discovered in sentence 2? Is it possible to turn this sentence into the passive? "She has been doing the washing for two hours". The washing has been done ?

1)Callie is a 16-year-old girl.She is special because she is one of the youngest people in Britain to win the lottery. She was with her boyfriend when the lottery results came on the television.
2) She checked her numbers and found (out) that she had won nearly £2 million.
3) She was so excited about her win that she started to scream and jump in the air for joy.
4) She said she was going to go on her first holiday abroad, perhaps buy a car, take her nephew to Disneyland and her forster-parents to a huge shopping trip.
5)Her foster-parents took her into their family for a period of time. They fostered her.
6) If I were she (or in her place), I would make a journey around the world/go on a cruise around the world/ buy expensive designer clothes, buy myself a Ferrari, donate some of the money to a charity, to needy children, to people affected by serious diseases.
the day. Thank you

1) OK, just needs a space after the first sentence.

2) She checked her numbers and found out that she had won nearly £2 million.

3) OK

4) She said she was going to go on her first holiday abroad, perhaps buy a car, take her nephew to Disneyland, and take her foster parents on a huge shopping trip.

5)Her foster parents took her into their family for a period of time. They fostered her.

6) In her place, I would make a journey around the world/go on a cruise around the world/ buy expensive designer clothes, buy myself a Ferrari, donate some of the money to a charity, to needy children, to people affected by serious diseases.

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"If I were she" is grammatically correct, but almost never used. Only very stuffy people would use that phrasing!

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'Is it possible to turn this sentence into the passive? "She has been doing the washing for two hours."'
I wouldn't -- and the reason is because of the present perfect verb tense, has been doing. Present perfect is used when an action began in the past and continues into the present. If the action is still continuing, it can't be passive yet, can it? =)