So...

I know that with knockback, figures aren't affected by terrain they pass through, due to the wording that they move 3 spaces, not 3 movement points worth of spaces.

With this caveat in mind, my heroes raised a pretty **** good question I've been unable to find an official answer to in regards to Tahlia-

Is her free movement taken in the OL's turn due to a ready-guard action restricted by terrain? Common sense says yes, and we play that way, but the ability clearly grants her the ability to move "a number of spaces", and not "a number of movement points" (which is why we don't let her suck down potions on her guard, etc)...

Has this issue been raised before?

yes, its effected by terrain. Knockback has almost a paragraph describing how the character is 'flying' through the first two spaces and so isn't affected by obstacles and traps along the way, but 'lands' in the third space which must be clear of obstacles and takes any related penalties for landing there.

Tahlia receives effectively a number of MPs equal to her speed (this can vary, thus they didn´t give a fixed value) - she can use them for any legal purpose. This had been clarified by Kevin Wilson in the last forum.

She enters all the spaces she moves through, so the OL can play traps on heras usual.