Chargers come in a lot of charge rates. If it is a low-rate charger it will take forever. If the cbarger she has is old, it might be slow by design.
Another possibility is the charge cable. If it is a very long or very cheap cable, it will not charge at full speed because of the added resistance in the cable.
The last thing to check (that bit me the last time I bought a phone) is if Smart Charging is turned on in the phone. It is a fairly new feature where it intentionally charges extremely slowly and only to ~80% until it *thinks* you are about to unplug it so that the battery doesn't sit at max charge for a long time.
On my current phone, that meant I could plug it in at 3PM and it would gain 5% charge before bedtime. If I got up at my normal 5:30, it would be consistently at 80%-82%. If I got up at 8:00 (when it apparently thought I should), it would be fully charged.
Turning the smart charge off now makes it charge at full rate whenever I plug it in and lets me manage the battery myself.
