Hope that answers your forward range questions, note sheik's hand is inside pichu's uptilt hitbox there.
You should know pichu is on frame 12 there and sheik is on frame 6, so you kinda have to be act before her to beat her in that way
also pichu's jabs on a shield have only frame between hits when the opponent isn't in shield stun, only thing is a light shield will get pushed away, and I don't know how you could follow that up, I'll look into that more
Update: I'm not sure what you're looking for in the shield pressure area but heres some info that might be useful
~continuous jabs leave opponent in shield stun for all but 1 frame in between, impossible to escape without the shield just being pushed away by the jabs unless they take a hit, they can buffer jump, roll, spot dodge... all will not but them out of the way/give them invincibility soon enough, but in the end they get jabbed... and if they're at low % you can jab them a couple times and at 100%+ or so you can act a few frames sooner than they can so you maaay be able to follow up with something useful..
~fair hits 4 times and leaves the opponent in shield stun for all but 1 frame in between just like the jabs, if you time it reeally well on a light shield you might be able to act before them if they don't buffer an action, could follow up with jabs to really hurt thier shield
~if you nair their shield on the last frame before you hit the ground you will be able to act before they can and can probably grab
all that and its all not very useful I don't think, but pichu's shield pressure options are pretty terrible, remember though, even perfect pillering is escapable... and even perfect JC shines will push your opponent away
tell me if theres anything else I could look into for you along those lines
Next: You may know this, but Pichu has only 3 moves with any priority/range worth mentioning
uptilt-above and in front
uair- behind, above, and in front
fsmash- in front
...thunder I guess
Shieks dair is reeeeeally terrible (her foot sticks out the bottom of the hitbox), she's really weak from below so if you space well you should be able to juggle her really well, your utilt and uair both beat her dair range-wise, and the only other options shes got left is DI or airdodge, airdodge you just gotta watch for and punish, and she can't DI far enough away from you usually. She could DI of stage but shes gotta come back and you can edgeguard. Only thing is its hard to go from a uair juggle to a kill move.
Hope something there helped, Pichus a really bad character and doesnt have very many good options... if any