Is she making this up?

So my friends been wanting a baby for a while now, and this morning she texted me saying she’s pregnant. She has no bf so I asked her when’s the last time she had sex. She said exactly a week ago and that was the only time she’d done it. I’m thinking, how can u be pregnant after 7 days, the egg wouldn’t have been implanted at that point and you wouldn’t have gotten a positive that early. Am I tripping or does it sound like she’s lying?