For Ike
-Make sure your Nair conversions are on point. Lucina doesn't rack up damage or have kill confirms as strong as Ike does so take advantage of that
-Don't be super obvious with Nair. I don't know what your GSP is but in Elite a lot of people have been parrying consistently. Make sure to use Tomahawks and Bair timing mixups so your opponent doesn't get too comfortable shielding your aerials.
-Outspace her whenever you can. Your Fair and Nair are a lot bigger than her aerials so take advantage of that when she tries to challenge you air to air.
-Don't get juggled. You'll have a bad time.
-If you're offstage use quick draw. Mixup going high or going to the ledge so you don't become predictable. If you use Aether you're probably a dead man. Air-dodging to the ledge is also pretty good.
-If she drifts too close to the ledge run off and Fair her. Sometimes this can catch people off guard since Ike's edgeguarding isn't the greatest. You'll only really get one chance at this but anything can help.
For Plant
-Try to bait your opponent into approaching. If you try to force things you'll just get eaten up.
-Use down special when your opponent is rushing in. This is mostly a gimmick but it works best when your opponent is rushing in and can't react in time. Don't overuse it though.
-Don't worry too much about having higher percent. As long as you don't run into a Fsmash or get edgeguarded you can outlive her pretty comfortably. Her up throw won't kill you until ~200 whereas yours will kill at ~150.
-Spike ball is okay in neutral but don't overdo it too much. Use it when you think she's going to jump in or if she's on the other side of the stage. Also some people forget that you can throw it short AND far. Use that to your advantage.
-Ridiculously outplay your opponent. This is a pretty rough MU. You'll really have to outplay her to win.
For D3
-Make sure your ledgetraps are on point. This is D3's best asset IMO so make sure you abuse it as much as you can.
-Gordos are pretty good in neutral since they force approaches. Don't spend ALL of your time running away or dodgerolling since that can get predictable, but you do want to play the keep away game. Throw your projectile, pay attention to what options she favors to get around them, and throw out attacks when you get a read on what she wants to do.
-Use your moves that outrange her. His Ftilt, Fair, Uair, Bair, Fsmash and Usmash have more range than most of her moves. They have more recovery but as long as you don't spam them you should be ok. Utilt is also pretty good.
-Get out of disadvantage safely when you can. His multiple jumps and fastfall are great at getting out of disadvantage. Stay out of her range and wait until she makes a commitment (either Uair or Utilt).
For Chrom
-Don't use Aether it will get you killed. Drift and air dodge to the stage. If you think she's going to intercept you, either throw out a Fair or use counter then use Aether. If you're really far offstage and you think you'll get edgeguarded no matter what you do, use an Aether suicide kill. It sucks but that's what you get when you choose Chrom.
-Don't overuse DED. It's not that great for Chrom and he has better ways to rack up damage anyway.
-Get good with his BnB combos. I see a lot of Chroms playing him like Lucina (spacing out one or two hit moves and resetting neutral over and over) for whatever reason and he has a LOT more combo potential than she does. Take advantage of this.
-Use his kill confirms. Seriously, don't play Chrom like Marth or Lucina. Learn jab>attack cancel Bair. It's awesome!
-Use your speed. Chrom and Roy are more faster than Marth and Lucina on average so use that to your advantage. Don't engage her if you don't have the upper hand. Make them work to hit you.
-Most of your moves have just as much range as she does so don't worry about being outspaced.
-Space out your moves on shield. Since you don't have to worry about Roy's sour spots make sure to space your moves at max range. This will protect you against Uspecial OOS and Shield grab.
well those are my tips.