This topic from Long and Short Reviews was a tough one. Mother characters aren't ones I tend to notice and I also watch a lot of horror, so I've seen a lot of mothers who were utterly horrible, abusive or absent entirely.
Then I remembered Rosa Vasquez from Shazam!
The parents in Shazam! are foster parents who run a group home for foster kids. Given superhero films are also famous for having broken family backgrounds and foster families are also often portrayed as abusive, it is extremely refreshing to see Rosa written and played as a loving, caring mother who works hard to provide a secure family environment for her foster kids.
So who are your favourite mothers in books, TV or films?