Actually, there's some debate over whether or not Healing by a same-gender channeler will really cut the strength in half.

Many of Siuan's quotes are more refering to her level compared to other Sisters and her standing with them as far as pecking order goes, and that if she could be Healed even half again as much she'd be half her old standing... Keep in mind that Sisters are all very similar in degrees of Power strength, for the most part, even if there is tiers and levels.

:) Also, it may also depend on who's doing the Healing, as well.  Although Nynaeve does seem to have a Talent for Healing, it's possible there's a separate Talent for dealing with the ability to channel, and that some channelers may just have an easier time healing severing - or perhaps severing at all! - than doing normal Healing...  *shrugs* Though there's no evidence of htat.

The Finns held her captive from the moment she entered the doorway and destroyed it.  Before that, she had a great deal of strength in the One Power.  Once she became held by the Finns, however, she had been burned out by the doorway ter'angreal, and thus was no longer strong in the One Power.

I take it there's more to the story, of course - she perhaps died eventually, perhaps after attempting escape, and thus was able to be reborn by the Dark One.  Moiraine wouldn't have died, obviously, so she is either cooperating with her captors, or is getting by some other way or another.  *shrugs*

As for the bond, it is indeed as was said: it snapped and refixed on Myrelle.  After all, Myrelle mentions later to Egwene that she's saved a few warders this way, from what I remember (though I'd have to reread that section to get an exact quote).  At the very least, even if it was unorthodox in that she (a) passed the bond on automatically (although how to do this is presumably common knowledge - they didn't seem to flap about this at all) and more importantly (b) did it without Lan's permission.... the fact remains that she appears to have done similar before, and doesn't really seem to think there was anything strange about this particular case aside from fears of the punishment she'd face for doing it behind the warder's back, so to speak.