I certainly like to try all my tricks out on my girlfriend first - and she's always keen for me to explain how they are done, but rather than tell her straight off I perform the same trick repeatedly - maybe from different angles - just so I can see how far I can take it - how many times I can perform it before it gets particular obvioius.
I hasten to add that for everyone else I try and limit to performing each trick only once.
I also let her examine some of the tricks that are so called 'partially examinable' (scotch and soda/cig thru coin etc) after I have perfromed them - so I can get a little feedback on how much scrutiny exactly they can come under. This I have found very helpful.
So yes i find it helpful to let her in on my secrets - but I make her work for it
I also find it useful to have her supply me with coins etc sometimes - it may not exactly be the same as getting a coin from the spectator, but it can be less obvious than using my own. (She looks so innocent).