HI Thezephaniah, and welcome to the forums. For those who don't know (like myself), you mean the character in 'The Walking Dead' played by Lauren Cohan.
A quick google suggests the shirt is branded 'H by Bordeaux' so you might have more success if you contact them directly. I don't know when she wore it but it's likely to be a past season style. Good luck, TV and film-worn fashion is often very sought after.
It would be easier to look for something similar, eg '70s-80s florals ala Laura Ashley. But they won't be screen-accurate.