No notification of rent law changes

Hi all, but of a general question here, daughter's landlord has requested a meeting tomorrow, reasons unspecified. She is understandably worrying as eldest child just started school, youngest shortly into nursery etc, busy times as young parents. Hopefully it's just to request a rent increase (not great but happens), but we think it may be an announcement of intent to sell. Landlord didn't send them any notice of the changes in the rent act which I believe was mandatory, wondering if this will affect their position legally? Any and all constructive advice welcome as always, cheers.