I have limited experiences and may not have the slightest ideas of pro tourneys, metagames and what not but I think Zelda is being downgraded for political reasons :D. But seriously, after playing with her some more she has a wide range of capabilities not seen in better ranked characters. She has a couple of major flaws which may make her seem super vulnerable and crappy but here are some ideas I want to bounce around:
1. Create a buffer zone using repeated combination of din's fire, nairu's love, jab in that priority. If you keep bombarding your opponent with those movies they'll be forced to roll shield in order to come close to attack you (assuming projectiles are being deflected w/nr). As soon as they get about zelda's arm link close you can do din's fire if they're a slower/bigger character and start a juggling combo, or do a grab move without the specific intention of really grabbing which might throw them off and make them roll out of your area and help maintain the buffer zone. If you're able to gram them hit them with a smash move while grounded and then teleport. Rinse. Repeat. If you're not able to grab, however, and you're hit, allow yourself to do a quick recovery swipe, do a quick jab A and teleport out.
2. Zelda has one of the best edge guarding techniques in the game. Hands down. You have Din's fire (a projectile) + Nairu's wind (teleport attack if done properly), and of course all her smash moves. I agree with Aznfinesse that spacing and timing are key, but there are so many options.
3. Psychological games. Keep confusing your opponent by transporting repeatedly around the stage but try to keep the the destination transport on the ground so u don't have to deal with lag. You can also confuse them with Zelda's grab move, which is an excellent setup to execute combos, and will keep them rolling away rather into you.