Don't rush into the electronics. Ruby and you haven't had a chance to break a sweat yet.
C'mon! This is fun, and you and Ruby can do this, too! Start out in your nice, calm, boring yard.. no kids, nothing. Practice COME. If Ruby is NOT at all dominant, use food, or a toy reward. If Ruby is slightly pushy, no food. At any rate, always use wild enthusiasm only when she gets to you. YIPPIEEE!! A party every time she comes? Cool beans, Mom!! When all is perfect, Practice COME when there is a kid zooming through the yard, or you are sure there is a squirrel in the garden, or the neighbor is using his weed whackah. (sorry.. originally from Boston here).
Perfect? Wow! Next, onto the BIGTIME!! Practice your recall in the most ho-hum, dullsville, boring field that you can. Darn.. poor Ruby, not even a jogger in sight! Use a longline.
Next, go to a busier field or the park on a dull, quiet day. Longline, and practice COME.
Finally, the park on a busier day.. eventually, a Saturday, oh my! Use that longline! Lotsa enthusiasm as she gets to you! YIPPIEEE! Use a treat or ball if you want. You are building a reliable recall in the midst of joggers, bikes, other dogs, running kids, babystrollers, and folks dribbling icecream cones on park benches! Go for it!