3) She thinks about Peter all the time is synonymic to She always thinks about Peter-the verb "think" here states a fact, this is why Present Simple is used.
4)However, this variant is correct, too. We can use Present Continuous with "always", "constantly", "all the time" to stress the fact that we are really annoyed by something ( a different shift in meaning). It's equal to "He's always complaining about his life" (he complains about it far too often than other people do)
5) She is thinking about Peter now (Pr. Cont. is used to underline the process that is going on at the moment of speaking)
6) Wrong. The key word is "now" tha indicates the usage of Present Continuous.
All the best,
Student or Learner