The answers to your questions are already in your OP:
either shit on or outscale LB. Here's some examples:
If LB can QW or QE you, you can EQW her without taking much damage. If you die to her after 6 it's your own fault, even then you'll still exchange kills from your dots because she's that squish.
LB's so squishy that your Q poke actually sticks to her and whittles her down hard, and your Q bounces will outrange her. If you can E her during her W, you will blink to her starting location and avoid all her W damage. Place a pink ward or trinket ward under your turret so you can always Shunpo back if she tries to go in on you and you aren't healthy enough to be stuck between her and her turret. Rush
and rank Q>E>W>W>W>R>Qmax to make sure you have enough aoe to secure a kill if she splits.
Q her if she tries to W or E. Shield if you get marked or chained. Poke the living fuck out of her with E.
Should be super obvious. E her directly and you win. Zone with Q and W. Save R for her W. Q at your feet when she uses W, and she won't be able to finish her kill combo OR teleport back. You fuck her so hard.
Also obvious. She's super weak to being pushed under tower and denied CS and roams. Heimer's the master of this. She also has no way of killing turrets without taking TONS of damage, especially if she ranks W first (like always) she will take turret damage for the full travel time.
Sit on your stun for levels 2-3 and Q or W if she goes in on you. E if you get marked. At 6, Q stun her into RW for freelo. Follow roams and pick up some early swifties to dodge/chase/follow before upgrading to Sorcs later on. Grab a Negatron if she gets fed by jungler or side lanes.
She can never kill both you and your egg. Play safe til 6 and then farm her ass afterward. Q when she uses W, but she will be using all her spells under tower.
All skillshots LB can't W through, and charm pulls her out of W. Ahri's QW mean LB can't hide behind minion packs, and R makes you basically juke-proof.
RE her W and she's dead and you take no damage.
Soldiers chunk her so hard that she'll be at half health just trying to get in position to QW you. You crush her.
You can Q or W LB's W or shield or ult yourself if you get marked. Lulu never loses to Leblanc unless the Lulu is literally braindead.
Obviously.
Obviously.
Your Q and W outrange her, and your QE and E knock her out of her W. If she tries to kill you at all, you can hit R to almost 1-shot her, and she can't juke your R damage at all.
You can die if you aren't careful, but you can easily out-poke and out-push her very safely.
You outrange, outroam, and outpush and can stun her out of her W. In fact, you can force her to back off just by cycling Pick a Card if she's looking thirsty.
She can't W through your stun on the dash, and you 1-shot her with R pretty quickly since she stacks AP so hard.
W her W and crush lane.
E her W. Stand right on top of 2 plants and troll the fuck out of her auto-target Q if she's looking thirsty. Your ulti can cover the entire distance between her W start and end points, so she has no way to get out of the area without blowing her mimic W to get out of dodge.
That should help. Also, the fastest way to find out how to beat a Leblanc is to play her. Even if you lose hard early, patience and utility will usually win you the game, which is why her win rate is so low despite being rather strong at the moment.