Unless you plan to show your long haired piggie (in which case you'll need to wash/dry and put the fur up in paper rollers) then trim the fur round her bottom for her own comfort.
They are messy little animals but its really not nice for her fur to hold all the pee/pooh, they can get sticky and stinky quickly. They like to sit in their own waste and their bellies ate low slung . . They should groom themselves (provided they can reach - you need to keep a check on your guinea-pigs weight to make sure they are agile enough and not hampered)
You can wash them (Gorgeous Guineas do some lovely ones), I used Cedarwood and Lemongrass to bond our two pigs , but I have Posh&Go for more conditioning.
We have a longer haired girl , we do keep her bum fur trimmed a bit and she needs the occasiononal bum dip.
The main advantage to her longish bum fur is our pest of a boar cannot get near her 
Drying them i the tricky bit . Our boar is dry as soon as he comes out the water
but I used a cool hairdryer on the sow.
If you trim , keep your fingers between her skin and the scissors. If you dry , keep you hand between the fur and the dryer .
Keep a close check in summer , flies (Flystrike) will be a risk if she's mucky. Keep a check on her droppings . Any loose pooh will get matted in her fur.
Your new baby will be a while till her fur grows but get her used to being combed when she's little .
Our pigs are a Teddy and a long haired (she's not Peruvian though, not sure what she is) My smooth was much easier 