They still don't know who will they put in this role, I think she can be anyone from their group or even stranger who will appear in last episode of this series.
And do only I have this strange similarit to Friends series when watching it?
Hmm doub't it will be Robin as "Future Ted" says "Aunt Robin" and Lilly we know It isnt her as they show a scene from the future were she is still married with Marshal :L.
I think it's going to be someone new that will show up in the last episodes of the series =P
I really want it to end to know who >.<... But at the same time... I don't want it to end! Ever!
I loved her on Buffy...until she turned into a lesbian and decided to kill everyone...
TBH, the first 4 seasons and the last season of Buffy are the only ones worth watching. The rest is just to know what happened in between. (There are a few choice episodes in there, though.)
...Moar hannigan
EDIT:
Wait, this is about How I met your Mother?
Eh, it's an ok show. Hannigan makes it better.