Except the Stargate would be broken; or some peril would prevent her from getting to it. And then when the TARDIS is used to escape the peril, then they find out *its* not working quite right.

OR they could use the TARDIS to get to another Stargate location. And the Doctor's casual knowledge of where most of the Stargates are located rouses her suspicions and she decides to hang around and find out if he's a threat or not...though that's not really a Sam thing...