There might be such a fanfic, but it's difficult to say for certain. Fanfic writers come up with all sorts of creative and often complex storylines. However, these specific elements of Daenerys being pregnant and Varys poisoning someone might be a rather unique and perhaps not overly common combination in the world of fanfics. It could be that a writer has explored this idea for the sake of creating a new and unexpected plot twist.
One possible plot could be that Daenerys' pregnancy is a cause for political unrest. Varys, being poisoned, might have some knowledge about who is behind it. Maybe he was poisoned by someone who wants to use Daenerys' unborn child as a pawn in the power struggle. His death could then set off a chain of events where Daenerys has to fight even harder to protect her child and her claim to the throne, all while trying to figure out who killed Varys.
I'm not sure if there is a specific fanfic exactly about that. There are a vast number of 'Game of Thrones' fanfics out there, and while the themes of Daenerys' potential pregnancy and Varys' fate (including being poisoned in some storylines) are common elements, it would be difficult to say for certain without a more in - depth search. You could try searching on fanfic - specific websites like Archive of Our Own or FanFiction.net using relevant keywords.
One possible plot could be that Varys poisons someone who he believes is a threat to Daenerys's unborn child. He might be acting out of loyalty to Daenerys and her future reign. Maybe he poisons a political rival who has been spreading rumors about the paternity of the child or planning some sort of harm to Daenerys during her pregnancy.
Well, it could be that Varys thought Dany was becoming too much like the tyrants she opposed. So he tried to take actions against her. Dany, being a powerful and often ruthless character in these stories, wouldn't tolerate such betrayal and thus killed Varys. For example, if Varys was spreading rumors about Dany's sanity or her ability to rule, Dany would see him as a direct threat to her claim to the Iron Throne.
In the 'Sansa meets Daenerys fanfiction', it's possible that their first encounter would be tense. But things could change. Sansa might be impressed by Daenerys' strength and determination. Daenerys, on the other hand, could see Sansa as a valuable ally. They could start a new chapter in Westeros where they combine their skills. Daenerys could bring new ideas of justice and equality, while Sansa could ensure the stability and traditions of the North are maintained.
Well, perhaps they could form an unexpected alliance. Daenerys, with her dragons, and Ghost, the direwolf, might team up to face a common enemy. They could use their unique abilities to protect each other and those around them.
There could also be other supporting characters that play important roles in the fanfiction. For instance, Tyrion Lannister might be there to act as an advisor to Daenerys during her encounter with Jon. His wit and political acumen could influence how the meeting between Jon and Daenerys unfolds.
In such a fanfiction, they might initially be hostile. Daenerys, with her dragons and army, could pose a huge threat to Cersei. Cersei, being the shrewd and power - hungry character she is, would likely try to outwit Daenerys. Maybe there would be some intense verbal sparring between them as they both try to assert their dominance over King's Landing.
In this fanfiction, Arya could potentially become an ally of Daenerys. Maybe Arya would be impressed by Daenerys' dragons and see her as a powerful force for change. She might offer her skills as an assassin to help Daenerys in her quest for the Iron Throne.