Keith, I wouldn't advise changing out the soil. Citrus have very fine feeder roots and the damage you'll do if you change out the soil will very likely kill the plant.
Just flush the soil with the soapy water solution before she brings it indoors. Soap kills off a lot of bugs. You can also flush with diluted peroxide if you're still worried - buy a bottle of it at the drug store, and dilute 1oz. of that with 32 oz. of water. Water that right through the potting soil and pour it away.
Yes, she's definitely over-fertlizing - the bottle of fert says once a month. It's a little tree, but a pretty big plant all the same so she needs to keep watering to keep it moist. They don't like to dry out. It shouldn't sit in water, but once the top half inch or so of soil dries she should water thoroughly again - enough so that water flows out the bottom of the pot. Tell her to stick her finger in the soil to test for dryness.