She's always had veins. As to why they're "showing up" now... who knows? Maybe she lost some moisture in her skin and it's a bit thinner than usual. Maybe she's lost a bit of pigment. Maybe they've always been there and she's just now "noticing" because she thinks she might be pregnant and is reading too much into every little detail of her body.
If she's having pain above her belly button, that's nothing to do with pregnancy. Your uterus is inside your lower abdomen, right above your vagina. It's not near your belly button. A sharp pain on ONE side could be worrying - it could suggest an ectopic pregnancy, which means her baby is growing in her tube instead of in her uterus. But pain on BOTH sides? Not to do with pregnancy.
I don't think she's pregnant. I think she thinks she might be, and is freaking out. Tell her to take a test and relax.