It all depends on your priorities... do you want the fastest path to being together permanently or do you want her to spend the summer there? If the former, have her come now, get married and start the process for the I-130 as soon as you get married. If the latter, wait until summer, get married as soon as she gets to the US, file right away and then enjoy the summer. I was thinking maybe you go down there and get married and start the process as soon as you get back and maybe still get the summer trip, but CBP may give her trouble coming into the US with an I-130 pending. It's a tough thing to try to decide....