She could always Thaumaturgy the door open, but that would kill any stealth. Probably best to wait on the muscle to come help.
Minor spoiler, but Kntoran is right. The makers of this door wanted the Giants who entered to feel the weight and be reminded of the solemnity of this place.
And so we're talking about a massive slab of stone that weighs about half a ton. The hinges they're mounted on are very very good, but even if no friction was involved at all, that's a lot of mass to move.