I figure they know that Annie can only power her suit for an hour a day. If they are going to keep testing how to make it upgrade, they have to ration her- and have other tests to run once she's out of power.
She was putting something inside the suit. But she's too short to reach into something her own neck height, so Tabitha is lifting her up. I figured that if they wanted to fool the suit into thinking she was inside it, you'd have to have the power source inside the suit, as well as the whatever is imitating her vital signs.