#1 - correct. I would change "whatever" to "what", and "is" to "to be": "She seems to be good at changing her look to whatever she believes to be most attractive in a given situation." #2 - both are correct but both sentences are weak because the sentences draw no connection between "attitude" and "person". Attitude about what? "I hate seeing people change their attitude towards someone based upon apparent wealth". "Change" is better than "changing". The present participle is correct but adds nothing to the meaning of the sentence. It's better just to use the verb.