Can’t stop thinking about this request

A lady gave me £20 to pay for ~£8 shopping then asked for £50 cashback. I said “You have to use a card for cashback.” She says “Really? I’ve never heard that before here.” I said “I can’t give you money for free” she says “That’s not what I mean. Whatever don’t worry about it”

I don’t think this was a scam, I see her a lot and she’s a normal, mostly quiet 60ishyo woman.

I don’t think she was on drugs, I can usually tell plus doesn’t seem like the type.

I don’t think it was a mistake, she seemed to know exactly what she was asking me.

What on earth is going on