I've never seen what you are experiencing, but I have seen mama guppies become very very ill when it was time for them to birth their babies. If they don't come out, the mama would either re-absorb them (I'm guessing) or die trying to expel them.
When I was about 15 years old, I had a mama guppy in severe distress trying to deliver. A whitish lump appeared where the babies should be coming out, and she was dying quickly. I took a razor blade and gave her a caesarian! Some of the babies lived, but the mama died of course. I figured it was better than letting them all die, and I certainly don't advocate this procedure for the squeamish. But since this is SUPPOSEDLY an open forum (as opposed to, say, an ARTICLE), I'm sharing my experience with the hopes that despite all the flack I'm assuredly going to get for mentioning giving a guppy a caesarian, it *IS* an option when all else fails. Make the incision quickly, and squeeze her sides gently, and make sure you're holding her over the tank.
Since that time, I've not done any fish operations like this, I've F.-L.-U.-S.-H.-E.-D. the dying fish before it died in the tank.
Good luck to you and the mama guppy and her brood, in whatever course of action YOU choose.