they are good guns, i got rid of mine and ended up with a smk xs78 although i prefer the crossman you have just got to watch c02 for the cold as below a certain temperature they don't perform well, they will kill all manner of small vermin
vetzyme bedding is good mate as you can put it in the washer and it dries like new, just keep feeding her the same food but a bit extra as it will take the weight off her feeding pups
Make sure she is getting a bit extra food and less excersize, make sure you get her used to the whelping area before she is due so she is comfortable in it. Terriers normally whelp without any problems but pre-warn your vet of her due date just in case. Good luck with your litter