Take a picture of me/for me (which preposition better translates)?
'给..照相' means 'take a picture of ..', so your sentence means 'can you take a picture of me'. 

The verbatim translation for 'do [something] for [someone]' is '为..做..', but in your scenario (asking stranger for help), it is more common to say '帮..做..' (help [someone] do [something]), so 'can you take a picture of her for me' would be '你能帮我给她照相吗？'