Question: having seen a few episodes of Voyager, I have seen a discrepancy. Why does Seven need to regenerate, but Picard was able to completely recover?

Same answer as always.

Because the writer gods declared that it would be so.

Maybe she has to regenerate once a month, you know the "woman" thing.

Picard was only Borg for a few days. And he was quite free at that. He was Locutis. Not just a standard Borg. Also, he still has some parts in him. If you watch in First Contact, Picard says that he still has some of their machines in him.

Seven was a Borg for a long time. She is dependent on regeneration. She really doesn't have to. But she chooses to because its more efficient.

Maybe to avoid all of the randy men aboard the ship. 'Sorry, I have to recharge, maybe we could do something later?'

Think submarines...out at sea for months...then put a woman there. What else is a woman to do?