I had the astonishing feeling of "Hmm, this is pretty good ... RON! DON'T SAY THAT TO YOUR SISTER, YOU ARE MAKING THIS INTO BADFIC! ARGH! BADFIC! STOP IT!!! ... oooh, nice plot twist there..." -- in short, not reading it as fan to canon author, but reading it as fan to fanfic author on an equal level of writing skill. I read LMB's stuff with a sort of awed delight and glee when she does things that I either would or would not have thought of doing with the characters and plot, as senior apprentice or junior journeywoman craftswoman to a well-established mistress of the trade.
I was not upset by any of the things I think JKR is going to have a hard time writing herself out of a corner with, because some much more talented writers with more polished writing craft are going to take her "oops" moments and fix them up, and I get to read it for free on the internet.
From a comment in the journal of ataniell93:
From a discussion about Tom Riddle's mother...
I have an interesting take on why she might have appeared to lose her powers. There's a long-standing idea that if/when a woman of magic gets pregnant, she loses her powers. I don't think it's so much that she loses them as that all the magic she has to spare beyond what's needed for healthy function of a magical person goes into the care, protection, and development of the baby.
So she may not be able to so much as light a candle when she's pregnant, not because OMG BABY = LOSS OF POWERS but because BABY = HUGE POWER DRAIN. Someone with a nice large amount of magic may be able to function quite nicely if they have more magic than a developing wizarding baby takes to develop, but someone whose magic was weak to start with is going to be horribly drained by pregnancy.
Dumbledore may not be used to working with witches who have so little in the way of power that they can't do anything while pregnant. And I suspect the magical needs of unborn babies differ from child to child -- it may be that a super-wizard like Tom or Harry needs a LOT of power, while someone of lower power needs less. (Which raises the question: if magic exposure while in utero is what's needed, perhaps there are a higher concentration of Muggleborn wizards in areas with a higher level of background magic, and a higher number of wizard babies born to Muggles who have been exposed to inadvertent magical contamination while pregnant?)
Say Riddle Senior had a property that had a great source of magic on it? And say that his wife was around the magic source a lot? That could account for Tom starting out as a very highly magical baby beyond what his mother's body could provide. Then, when she decided (while pregnant) that she needed to stop feeding her husband love potions, and she got thrown out, she no longer had that magic source at hand to nourish the growing child.
But babies are all need, and draw from a mother's body sometimes beyond the danger point. Without that magic, little Tom took more magic than was healthy for his mother, utterly disabling her ability to work magic, and eventually draining her to the point that once he was born, she died. Not for lack of will to be there for him, but from sheer physical and magical exhaustion.