I highly recommend the Oral History Society for lots of advice on interviewing individuals, including getting the conversation started, which recording equipment to use, etc.: http://www.ohs.org.uk/
If you know that you want to eventually add these interviews to Historypin, one of the biggest differences from more traditional oral histories is really trying to frame interviews to get interviewees to think about particular places, so that we had concrete (or at least general) locations to map audio clips to. With your relative for example, aside from where she was born, went to school, etc., some places could be:
-Can she remember where her family was when the war broke out?
-Where did she go to have a good time during the war?
-Did she help in the war effort in any way? Where?
There are many questions you can ask to pick out some important places from her time growing up during the war, so these are just a few suggestions. Hope this helps!