She's not very far along...a week maybe. She looks like she may have a bit of a fungal infection. Is that slimy looking stuff (toward her tail in the pic) attached to her body? Has she always been yellow on her abdomen like that?
I would be worried about your guppy as nosoup said she looks like shes got slim hanging off her tail - i suppose it could just be the pic but please have a good look at her
She's definately early on in her pregnancy as nosoup also said
here's some pics of my guppies they the ones with the squared off bellies are due anytime (they are approx 4 weeks pregnant)