It's possible for a woman to "spot" after conception. Sperm can live for three or so days inside her body. Some women know they're pregnant the moment it happens, some are very, very clueless.
Pregnancy's possible.
However, why don't you look for other things that may have caused her nausea?
Advice? I think you should drop the forty bucks for the Pregnancy Test and find out. Put your mind at ease, or work towards an amicable solution. It's gonna be what it's gonna be, but I guarantee you'll feel better having acted on it sooner rather than later.
Congratulations on getting pregown3d.