It is not acceptable to pay into the landlord's private account, the landlord MUST know this, so she can expect some trouble getting 100% of the deposit back....
In German speaking Cantons she needs to join the MieterVerband in the Canton where the apartment is located, (It costs about SFr 75 a year)
https://www.mieterverband.ch/
At the handover she can ask for a witness from the Mieterverband to be present, she will pay for this, (It costs about SFr 100 per hour) but at least the landlord cannot perform any more nasty tricks!
She should clean the apartment
thoroughly and it is best to use a steam cleaner in the bathroom and the kitchen. Don't forget the blinds or shutters!