Air conditioning units dehumidify as part of their process, and they do it quite aggressively. As soon as warm moist air hits the cold a/c coil any moisture in it condenses on the coil, drips off and goes to the condensate drain. Now if the condensate drain is clogged or its an all-in-one unit thats outside and not tipped at the right angle, condensate can collect in the pan and be reintroduced into the air.
Some more efficient air conditioners do try to limit the reduction of humidity to improve efficiency, since that moisture saps cold from the coil and then runs off into the ground as cold water. In fact, there are some new air conditioning technologies coming out in a year or two specifically targeted towards the pacific southwest that dont do very much dehumidification at all since the air is already dry. Those are expected to be 20% or more efficient that current a/c technology.
Dehumidifiers are essentially very inefficient air conditioners. They shoot to remove as much water as possible. So an average dehumidifier will take more energy than an air conditioner to remove the same amount of humidity. As a double whammy, they produce quite a bit of heat and blow it back into the house, which your air conditioner then has to work to remove. To get an idea of this, the next time you see a window air conditioner running inside a store, put your hand around the back and feel the blast of 120 degree hot air coming out of it.
The electronic thermostat will only save money to the extent that she can program it to automatically drop and raise the temperature of the condo during the night and during the days she's at work. Depending on where this is, how much temp change she feels comfortable with at night, and how much she works, she could save 10-20% on her heating and cooling bills. Or almost nothing at all. She could accomplish the same thing by pushing the buttons on the thermo when she leaves, returns home, goes to bed, and wakes up. Free. See what sort of results she gets.
Get a humidistat and see what the average humidity in the condo is. If its over 50% then something should be done about it. Either the air conditioner needs to run more, you'll need a new one that allows a humidistat and has cycles to run longer to remove more humidity, or you'll need a dehumidifier to reduce the moisture...but the electric bill is going to go UP in that last option, not down.