It's always worth running these things past a vet in daytime hours or they tend to worsen at weekends and after hours, IME!
Be sure to weigh your pig daily for the time being, and up your observations to see if this piggy is at the water bottle and hay as normal. Is she still running out as fast as usual when you crinkle a salad bag, open the fridge or pop her favourite veg in?
Any slowness to respond, increased time spent quietly sitting in one place and you need to be onto the vet right away today.
If she is active as usual, definitely munching hay and showing a quick and keen response with veg - if you are totally certain her behaviour is every bit as lively as usual - then be sure to start the daily weighing and obs.
As
@Bradshaw Piggies says, it can be something as simple as some hay stuck up the nose - but a week is quite a while for it not to be sneezed out - or it could be an allergy to dusty hay, wood shavings or any manner of things.
Be aware also, that if the cause is environmental (like a reaction to something in the cage) this weakens the pig's immune system, leaving them vulnerable to more serious infections so it is vital to get on top of it.
The vet is always a good call anyway to put your mind at rest, i think.