they are all very fussy about their nests (be them male, female, pregnant or not)
They will often change and rearrange it, adding oreven removing bits they don't want in their beds. Storing food inside the house is also natural behaviour, they keep it in there for midnight feasts
Females can become pregnant after 4 weeks of age, she probably would show serious signs of pregnancy by now!
Preganant hamsters (although i have never owned one,i talk from others experience) will be very hyper and sometimes quite grouchy. They will build up HUGE mounds for their nursery nests and store lots and lots of food. Someoneelse may be able to give youotehr signs of pregnancy.
But i'm pretty sure shes not, so take a big sigh of relief