How to interpret the Sorcerer's Flexible Casting ability that utilizes Sorcerer Points to create Spell Slots:
"...As a bonus action on your turn..."
Which doesn't go to say that every spell ever that takes a bonus action or action on your turn can't be used out of combat, but we can assume they stress this point due to its combat applications. Creating or burning spell slots doesn't have too much out of combat usefulness. You would interpret this as a combat ability, and an out of combat utility that can be useful in certain situations.
Each Spell Slot that you are able to craft through the use of Sorcery Points takes an amount of SP only acquired once you are of sufficient level to even have that level of spell slots available to you. So while you could never have a spell slot that's beyond your ability to use at the time, its primary use is replenishing spell slots that you've cast or otherwise used up in battle (as when you burn one to gain more SP so you can put them into a Meta Magic ability). They do not roll over , as it were, as taking a long rest basically returns everything to its normal state. Extra spell slots disappear, Temporary HP disappears, and any temporary buffs or bonuses that were applied through magical means disappears; unless it has an effective duration exceeding your Long Rest period. Flexible Casting spell slots are no different.
So yes, the rules don't say anything about not being able to exceed your normal maximum allotted spell slots. Taken as written, if you wanted to burn all your SP at the beginning of a combat to gain all those extra spell slots, you could do so, but yes; they are lost on a long rest. No slot hording for you!
I hope this helped in your interpretation of the ability and the rules. I have a Sorcerer in my adventuring party and I'm kind of jealous of his raw magical power. He's a beast with those Twin Spell and Quick Spell Meta-Magic feats, and we won't even touch on Magical Missile...
She can use the feature once, and then must wait until the next day
Note that the feature states:
Once per day when you finish a Short Rest, you can choose expended Spell Slots to recover.
Everything after that is just a specification of the maximum level and number of slots you can regain, but not necessarily the levels of the slots that you actually regain. From this excerpt, it is clear that there is no pool. You use this feature once, and then can't use it again until the next day.
In your example, scenario A is not allowed. She already used the feature to get a slot back, and so can't use it again. Scenario B is not allowed either for the same reason. However, if the wizard spends a slot and finishes a short rest without using her recovery, then she has it available at the end of her next short rest.
Best Answer
It doesn't create new slots, it restores a used slot, sometimes at a lower level
Pearl of Power states:
So you can only regain a slot that has already been used. But:
So, if you choose to regain a slot above level three, then it is effectively temporarily downgraded to level 3. That means, in your example, if you have cast a fourth level spell and no other spells, that temporarily you would have four level three slots and no level four slot.
What happens when you take a long rest?
After you take a long rest, all of your normal spell slots return (in your example, this would be 1 at 4th level and 1 at 3rd level). The extra 3rd-level slot you had created with the Pearl of Power has simply reverted to 4th level - as it was previously. This slot has not been 'lost' as at no point had you created an additional new slot, you'd simply refilled an empty one.
Using the Pearl of Power may have temporarily changed your build slightly but you never gained anything better than what you had in your original build - what you did temporarily gain was always equivalent to, or worse than, what you started with. So there'd be no benefit to this persisting through a long rest, and potentially a considerable cost (i.e. losing a stronger slot in lieu of gaining an extra weaker slot).