Again - if your uncle was saying that him and his wife couldn’t afford the rent, it was very foolish of her to co-sign a tenancy agreement under a lie that she’d live there. Did it never occur to her that if they didn’t pay the rent, she’d be co-liable?. Frankly, MUCH worse could have happened than just her name staying on the agreement.
Im afraid this is a case of “Play stupid games win stupid prizes”
She effectively took part in a scam so can’t be that surprised that your uncle behaved in a dodgy way too.
If you do contact the landlord I’d be inclined to leave the bit out about her never having lived there