Awww Congratulations (I know it's out of the blue but Congrats are in order 
)
Mum pig will get on with feeding her baby, they are very ameanable mothers and I have never heard of female GPs eating their young like some other quadropeds yes rabbits I mean you can do.
Baby guineas are much fuller formed, teeth ,fur,open eyes and able to waddle.
They are usually born fairly quickly (ours had three piglets within 40 minutes) so chances are there's just one, BUT keep a check on her- any straining, high temperature (feel her ears and paws) dull eyes, lethargy, not eating/drinking and any bleeding from her genitals , contact your vet.
Female guineas have a waxy secretion in season and after mating and until she cleans up, there might be some of this round her rump.
She would've been half way through (its 63-70 days gestation) when you got her.
Double check your other pig is a sow (they will mate again straight after birthing tsk ) and hopefully she isn't upduffed as well.
Then you need to decide the fate of piglet- it would work out well if it's another female. If it's a boar, you'll need to seperate him from mum (and aunt) when he's about 3-4 weeks , or he'll start showing an unhealthy interest. The sows will usually wean the piglets themselves.
And - contact your breeder because there might be other people getting a surprise present and it's not the best practice to send your pigs out pregnant 
And you'll get lots of 
squee and demands for pictures.
So
squeeeeee
Pictures