A lot of haters said that Tashigi is dumb for not recognizing Zoro because he carried three swords...
Here's the thing, in her wildest imagination she never thought that Marimo would be a kind hearted muscular handsome man. First impressions are everything. In addition, he is a swordsman which makes conversations flow easily when couples have shared interests which is why she opened herself to him. More importantly, he is humble and has insane guts with the Kitetsu swords.
Tashigi sees him as a formidable swordsman with strength, and honor. The fact that he is a pirate literally shook her views of what a great swordsman could be.
Can you Imagine her reaction if she learns that Zoro became a bounty hunter cause he was lost and hungry and needed cash ASAP ?