how to make my wife's mid 2012 macbook pro 13 faster?

She got a good new job so I bought her a mbp 13" mid 2012, and basically on her first day a co-worker had a newer 15" model with retina display and she's been kinda bummed out about it.

So I was wondering what I could do to make her's faster? I would like to get her the newer one but I didn't realize she would need it and how slow the mbp 13 inch is...if I just add 4gb ram and make it 8gb will it make a good difference? Or should I ebay the 13 and buy a 15?

IS the 13" MBP actually slow? Or is just a matter that it doesn't measure up (in size or performance) to the newer 15" rMBP?

If the MBP you have works fine for the tasks at hand, why would you be envious of someone else's machine and want an upgrade?