My sister shut off the gas to the water heater 4 days ago could this cause the water heater to leak from the shut off valve

The packing nuts to a shutoff valve are usually never tight even for ball valves. I'm asuming that this is the water in shutoff and it was a newly replaced ball valve.

The packing nut under the handle needs to be tightened. Remove the handle. Tighten nut. Put handle back on. Test if too tight. Tighten handle.

Damage could have also occurred when soldering next to valve.

Are you talking about Gas valve or Water vavle ?