The actress met her late ex-fiance Ledger on the set of the cowboy drama in 2004 and they went on to welcome Matilda the following year (05).
The couple parted ways in 2007 and a year later (08), the actor died of an accidental overdose in his New York City apartment.
Williams has since raised Matilda on her own, but she hopes to share the film with her daughter so the youngster can see her parents together.
She tells Angeleno Magazine, ""What does that movie (Brokeback Mountain) mean to me? That movie is many, many things... It is a piece of cinema history and I happen to be involved in it. There've been a few films that I have been so transported by the filmmaking that I couldn't focus... I felt like I got really close to the thing that I wanted to do and I was very proud... to be associated with it.
""I was just an actor who happened to be lucky enough to be in the right place, and it was the place where I met Matilda's father, and that is a lot. It was a lot. And it will be a lot for Matilda too, when she gets around to watching it.
""I will watch it with her, when she's ready. It is hard to imagine what that would feel like, but one day, yes, we will watch it together.""