Williams spoke to Porter magazine, out this Friday, about raising her child without Ledger.
"In all honesty, for pretty much everything else, I feel like I’m a believer in not fighting circumstances, accepting where you are and where you’ve been," she told the magazine. "In pretty much all senses, but one."
"I would be able to go totally down that line of thinking were it not for Matilda not having her dad," Williams added. "I mean, it just won’t ever be right."
Williams, now 36, and Ledger began dating in 2004 and welcomed Matilda the very next year. The two had already split in 2008 when he died at the age of 28.
But the "Manchester By the Sea" actress took a lighter tone when talking about how she handles all that comes with raising a little girl.
"Sometimes I think motherhood is really all about scheduling and cooking! It’s so different at so many stages. If you’d asked me three years ago, I would have had a very different answer. Now it’s like rainbows and unicorns and sunshine, but that’s just the place we happen to find ourselves in right now," she admitted.
She continued, "It is ever-changing. I feel like parenting is reeling your kids out a little more every day. You keep [the line] taut so that they know you’re there, but you grow them up so that one day they can leave you."
Matilda brings the three-time Oscar nominee immense joy and watching her grow is something she finds so much meaning in, she added.
"I watched [Matilda] warm in the sun, in her swimsuit, get on her bicycle and smile and wave as she rode off to go meet her friends. I went back into the house and sobbed because of this incredibly simple moment –- common everyday happiness," she said. "I really felt like in that moment, like wow, we’ve done it. Not only are we OK, she’s happy. Life has brought us to a place that’s not just surviving, but thriving."
As for dating, she admitted it's a "learning process."
"I feel really sensitive about it and certainly did not expect to be still dating at 36 with an 11-year-old. This is not what I imagined," she said. "But I’m also happy with myself and just because I might have a desire to be with someone."