anonnyscouse

It added a bit of ambiguity to Hoster's deathbed rambling, it's still likely that it was Lysa's abortion he was talking about but it is possible he had an affair.

The main objection to Mance writing the letter (as it is with Ramsey too) seems to be the heads on spikes reference as not being in context for a wilding (or a Bolton), but I don't recall ever finding out where in Westeros Mance lived before he took the black.

It's likely to be Sweetrobin, remember the Snow Winterfell Sansa built and he destroyed?

I think tansy tea is a likely explanation, but we do actually see a Tansy in ASoS a "buxom red-haired innkeep" Arya meets while with BwB.