Dig a BIG hole, (at least twice the diameter of the new pot) take the mixture you have dug out and mix with some sort of ericaceous compound, used to use peat, dont think you can still get it now, and plant new plant in that mixture in the BIG hole, dont use tap water in drought conditions unless you absolutely have to, if you do then get some sequestrined seaweed type liquid to mix with it. Top dress annually with ericaceous stuff and all should be ok.
Watch out for the leaves going yellow, that's a tell-tale sign all is not well.
HTH (she might even think YOU know what you're on about).