Main reason I ask is I would like to get a basic DSLR for the GF. There would be no post processing and shot in JPEG, but I would still like good quality photos for us. She would be able to use my lenses if she needs them, hence the reason for considering switching over to Canon at this early point if the JPEGs are better.
DSLRs will still produce better images even in auto mode
As for sharing lenses, Honestly, Dont do it unless YOU actually want a Nikon or something, if you're out somewhere and etc i find its better both of you have a basic set of lenses (18-55 and 55-250) as opposed to both of you sharing from one bag of lenses (Unless its like you're sharing the one expensive L)
But even still, she will have to learn one or two things, This came up with my Mom, She wanted to get some better quality pictures and that compared to her current point and shoot, I discussed the issues with her images (Namely they were all VERY noisy and grainy, lacked any "pop" and etc) and told her shed be best looking at a DSLR as opposed to a high end point and shoot, She ended up getting a D3100 and quite likes it, She went into it however 1. being HIGHLY technically literate to begin with, and 2. willing to learn one or two things about her dslr to enable her to use it correctly
If your girlfriend is neither 1 or 2, Then I suggest you take her to look at something mirrorless instead, She also might not like the weight/size of a DSLR or complain it isnt fashionable or something....The Nikon J1 is actually a really good option here for her as it really is a point and shoot with interchangeable lenses...any of the mirrorless out there will do but the Nikon is definitely the most "friendly" from what i've seen