It means she automatically - ie, when she was born - became a British citizen (by descent) under section 2(1)(a) of the British Nationality Act 1981.
She's still an Ecuador citizen, most likely, so may still need an Ecuador passport as well as a British one.
Your other daughter, isn't she British too ... unless she's your step-daughter? If so, why doesn't she also have a British consular birth certificate?
Note the exit requirements for Ecuador citizens under 18 travelling without both parents: http://travel.state.gov/travel/cis_p.../cis_1106.html