How do you deal with oily hair?

I couldn't find an existing thread about oily hair, so I figured I'd just start one myself.
My wife deals with extremely greasy hair that develops a pretty unpleasant odor, which means she basically has to
wash it every single day just to get by; by day two, it’s honestly unbearable. She works a standard office job, so she isn't really exposed to anything harsh like heavy sun exposure, smoke, or industrial chemicals. She's already tried almost every high-end shampoo
on the market and even saw a dermatologist, but nothing seems to make a dent. I guess if anyone else is dealing with similar
issues, I'd appreciate it if you could share what worked for you. Thanks.

I suspect that washing your hair every single day might actually be making things a whole lot worse, if you think about it, because the constant stripping away of moisture from your scalp could potentially trigger it to produce even more oil as a sort of defensive reaction.
It's also worth noting, perhaps, that having excessively oily hair can sometimes act as a little signal or symptom of PCOS.