Like bpatters said, two sneezes is nothing to worry about for her
URI symptoms are more excessively sneezing/ a runny nose/ become lethargic/ or eating less. If you've been sick, I think the general conclusion is guinea pigs can't catch human viruses, but it's possible for them to catch bacteria/infections. I'm quite paranoid myself and handle my piggies food etc as little as possible, keep my face away from them, and wash my hands constantly when I'm sick.
When I first got my Robin Hood he was about 6 weeks old and kept sneezing a lot (5/6 times in a day) , and I was SO worried. He showed no other URI symptoms, and after a few days the sneezes stopped. He's been the picture of health ever since!
We figured out what was causing may have been a mix of adjusting stress and this: when he drank from his guinea pig water bottle, his mouth was so little he'd end up getting a nose full of water as well, poor baby! lol We added a hamster sized one next to the guinea pig sized one, and he'd choose it instead; it stopped the accidental nose full of water.
Heat is much bigger danger than cold to piggies, the temps of your house sound like no problem at all. I use carefresh type paper bedding as well and it's never caused my piggies issues.
That's great she's eating carrots and red leaf--- try mixing in little bits of bell pepper now! Nearly all piggies adore it, and vitamin c is so important for them. The extra vitamin c they offer would be a nice precaution against her sneezes, too