If the mother allows she could pick up the baby and check for a milk band (white line) under the skin. It's good to handle the babies from day one, but you could let the babe be with mom for a while too, if she seems to be taking care of it fine...
Have her keep an eye on Mom... just in case there's more.
well its afternoon now so i think it would be safe to say that there are no more babies coming. did she end up with just the one? how is mom doing now? if the litter ended up being small (only 1 or 2) you'll want to keep and extra close eye on mom to make sure there aren't any stuck or any other complications. she will be a litter tired after giving birth but she should be her usual lively self by the next day.
a small litter is rare but is not unheard of. Iedani only had 4 babies and one died after a few days (i didn't have her when she was pregnant or rasing the babies so i don't know why the one baby died). the plus, if there are no complications and the baby is being well cared for by mom is that you don't have 12-20 babies to rehome. will your gf be keeping the baby or finding it a home later?
now, onto some information for care of the newborn and new mom. the mom will be nursing now so she'll need more protein to keep her and the baby fed well. a boiled egg or some scraps of meat would be appreciated now. getting her on a more protein rich staple like a puppy or kitten dry food would be a good idea too (some people say to keep to puppy as their nutrition is closer to what rats need and others will say kitten because of the added vitmins and even higher protein. personally, i would go with kitten first for a week or so to give mom that extra added boost seeing as she came from a pet store and they seldom feed their rats right). adding boost or ensure to the mother's daily diet would help as well, especailly in the beginning as she's likely undernourished from the pet store and the strain of having the baby.
you'll also want to start handling the baby for a few mintues a few times a day. you don't want to handle the baby so much that it doesn't have an opprotunity to eat or to get cold but it will need to human contact to be come the best possible pet is can be.
baby rats will not be able to control their body temeperature until about 2.5-3 weeks of age so make sure the cage isn't anywhere where it can get a chill or draft.
the baby's eyes will open at about 3 weeks.
you should separate any sons from mom absolutely no later then 6 weeks, 5 weeks is normally recommended. this is only to prevent mom from getting pregnant again, male and female rats can live quite well together if one or both genders are altered to prevent babies.
if you end up with a boy nad want to keep it with mom, he can be neutered as early as 8 weeks of age if he is of an average size for that age. if he's a large boy then there will be no problems either but he has to be a certain size before a vet can even preform the operation. simply because they don't have the tools necessary for animals any smaller.
if the mother is in a cage with multiple levels, you'll want to take the levels down. mom could try to take the babies into a higher level or hammocks and one or more could fall out of the nest and be injured.
i think i covered eveerything but if i haven't someone else is sure to fill it in. please keep us updated as to this little ones progress and we hope to see some baby pics up sometime soon too. *smiles* we all love cooing over the new pinkies
She had her reasons for eating it. It either wasn't healthy or it was deformed or something. She most likely had other babies but she probably ate them for the same reasons or they where already born dead. It's not to say she was a bad mother just that she sisn't have healthy babies.
Sorry for your loss even though you didn't know em that well...