Why does this brand new Beko washing machine slowly fill with water?

My mums new Beko (cold-filled) washer fills with water very slowly when it is not in use. This is our third identical machine - the first was damaged at the front upon receipt, and the latter two have had this problem with the drum filling over time. She said it fills quicker when the tap in the sink is run? I don't know how to tell if it a faulty valve on this model or a water pressure problem - is there a way to know this? she lives in a terrace with cold water tank in the attic, no such problems with the old machine, or perceived problems elsewhere in the house. If it is the water pressure what is the solution? She's just an old lady, I'm miles away and its really getting her down... me too! She now wants it sent back for a different model completely; but I'm concerned the next one might do the same thing?