Hi, a friend just received a 2 month double entry visa from the embassy in Canada. Does the double entry mean that she can just cross the border after the initial 2 months and then stay 2 more months or is it a reentry and she'll have to apply for another tourist visa in Penang. She wants to stay 4 months.Thanks.

It means she can enter Thailand twice. Each entry gives a max. of 60 days and can be extended at Immigration for a further 30 days each. (1,900 Baht)

She must make the second entry before the VISA itself expires, usually 6 months from the date it was issued.

Yes before the 60 days expires she exits/enters another country and returns for a new 60 day stay (and if a few days short can extend 30 days more for 1,900 baht).