An overbearing mother with a classic upper-class disposition, Camilla is the Lucille Bluth of the Traynor family. The only difference is that Camilla is a lot warmer than Lucille, once you get beneath the surface.
We get a pretty solid description of Camilla's personality as soon as Lou meets her: "A woman's face appeared, middle-aged but beautiful, under expensive precision-cut hair. She was wearing a trouser suit that I guessed cost more than my dad earned in a month" (2.21).
This gets at two major aspects of Camilla's character. First, it shows that she's a bit high-strung, though we don't necessarily mean that in a bad way—basically, she's Type A through and through. Second, it shows us that she's imbued with a sense of upper-class privilege. Camilla even says that she always thought that she was "not the kind of person this happened to" when talking about Will's accident (8.3).
But Camilla also has a lot of heart. As easy as it is to criticize her for the sometimes overbearing way that she treats Will, the truth is that no one does as much for him as she does. She's put her life on hold to make him as comfortable as possible. Does she always hit the mark? No way. Does she sometimes frustrate him? More like "usually." Still, Camilla deserves a lot of credit for the lengths that she goes to support her son.
Camilla even sets aside her reservations regarding Lou because she knows how much Will cares for her. It's pretty strange: though Camilla hires Lou, she remains skeptical of her for the longest time. Maybe it's because they don't click as individuals. Maybe it's because she thinks that Lou is after the family's money. Either way, Camilla manages to abandon her preconceptions about Lou because she knows that it's the best thing for Will. That's significant.
In a similar way, Camilla puts Will's needs ahead of her own by allowing him to go to Dignitas for assisted suicide. This is the last thing Camilla ever wanted to happen, but she lives up to her promise knowing that the alternative is much more painful. That's a selfless act. As easy as it is to perceive Camilla through the lens of our preconceptions of frosty upper-class British ladies, her character is a lot more complicated than this narrow view implies.