I'll guess at this. It's possible that she is a Lavender Ameraucana or Easter Egger chicken.
Lavender Ameraucana: These hens are known for laying blue eggs and have a distinctive lavender color in their plumage, which can range from soft, silver-gray to a deeper lavender. They also typically have a large, floppy comb, and their feathering is a bit more unique compared to other chickens. They are a breed loved for their beauty and their egg-laying abilities, (which is maybe part of why she was at a farm).
Easter Egger: Easter Eggers are not a breed per se, but a mixed breed often known for laying blue or green eggs. They can have various feather colors, including lavender, even grey, and may have a variety of comb shapes, often floppy. Since they're mixed breeds, Easter Eggers can have a range of physical traits, so your hen could very well be one of these!
Either way, it sounds like a beautiful and unique bird! She's lucky you rescued her.
Maybe she might be a little underweight? Protein and some vitamins will get her going on strong and then it will be even more obvious about what she is