No, she won't be playing the mother.
With that out of the way, we can report that Brooke Nevin will guest star this spring on How I Met Your Mother.
According to Fancast.com, the actress will portray Amanda, a romantic interest for Ted. She'll be his date at Lily’s birthday party, thereby continuing his awkward tradition of dragging new gals to major group events.
Nevin's episode will air in March. Among other shows, she's appeared on Grey's Anatomy, Eli Stone and NCIS.