Is a runt likely to have health issues?

[t1gg3er]

We have a litter of 6 pups with one being much smaller than the rest.  They're 12 days old & she's been around 2 days behind the others in development (skin pigmentation, fuzz coming through etc...).

We have 4 girls in the litter so my eldest son & his girlfriend will be having 2 & the other 2 will stay in a trio with mum.  My plan was to keep the tiny one so any health issues will be at our expense and, if anything went wrong (although I really hope she lives as long & healthily as any other gerbil), there'd still be 2 girls together.  However, my son's girlfriend really wants her.  

Is she likely to be healthy but just small?  If that's the case then I'm happy for them to take her along with one of her sisters.

You can see on this pic how much smaller she is (mottled one, 2nd from left) although she's just as active as her siblings:

[fysha]

In all my litters, both recent and years, and years ago, I've never had health issues with the runt. I have one right now from Kahla's first litter that I worry about because she is so small still, but she is healthy. She is six months old and 52 grams. Her sister from the next litter, at 4.5 months is, 61 grams.
I find as long as the mother/father and litter are healthy, the runt would be healthy, but then, things could/do happen.

[t1gg3er]

Thanks for that. I think I'll see how she goes between now & getting to 4-5 weeks when I have to decide who stays with mum before the 2nd litter comes (the other 2 girls will then move out with dad & the boys until they reach 6 weeks). At the moment she's doing everything the rest of them are doing. She's just very small. So if she's still doing well by then I'll say they can have her.