Personally, speaking for myself and no-one else, I think that letting her know from the outset that you are not interested in an exclusive relationship is a kindness, so she doesn't set up any false expectations.
You don't, in my opinion, need to bring up the word/concept of polyamory until the relationship or conversation takes that turn (although you should be prepared to have that conversation from the minute "non-exclusive" is mentioned...some women ARE looking for monogamous-husband material and, I think, have a right to know from the start that that is not what you are offering.)
Me: poly bi female, in an "open-but-not-looking" V-plus with -
MrS: hetero polyflexible male, live-in husband (23+ yrs)
Dude: hetero poly male, live-in boyfriend (4+ yrs) and MrS's BFF
Lotus: "it's complicated"
SLeW: platonic girlfriend + BFF
+ "others" = FBs, FWBs, lover-friends, platonic G/BFs, boytoys, etc.
My poly blogs here:
The Journey of JaneQSmythe
The Notebook of JaneQSmythe