If you're shffl'ing correctly zelda can't shield grab you, her grab is the slowest (non grapple/hookshot) grab in the game iirc. Make sure not to start your aerials too high up in the air, or it will allow her to do so. Use your move right before you hit the ground to decrease the time spent between hitting the shield and shining or jabbing or whatever. Also try to learn to space your attacks properly so that when you are landing from your shffl you end up behind her so she can't grab you. Careful not to get bair'ed if you do that though. Maybe throw up an up tilt right after if she starts to jump out of her shield to bair you. If you manage to hit her with a dair, try to chain a few together. At mid percents you can do this a few times, especially if you can tech chase decently. Towards the end of that type of sequence, you can look to pop her up in the air for a spike. I usually use that technique a lot against jigglypuff, but I find it useful against a lot of light characters like peach mewtwo and zelda.