Short answers, pulled from the story.
Cäcilia Weber (born the 23rd of October 1727, died the 22nd of August 1793) was the mother of Constanze Weber and the mother-in-law of Wolfgang Amadeus Mozart. Mozart married Constanze on the 4th of August 1782, making Cäcilia his mother-in-law.
Cäcilia Weber was born in Mannheim. She was the daughter of Johann Otto Stamm, a government secretary, and Sophia Elisabeth Wimmer.
Mozart first met the Weber family in 1777 when he came to Mannheim searching for a job. During that visit he fell in love with Cäcilia's daughter Aloysia, though she later rejected him when they met again in Munich.
Cäcilia asked Mozart to leave her Viennese boardinghouse when she realized he had fallen in love with her daughter Constanze. She made the request for reasons of propriety.
In a letter written in 1825, Sophie Weber recalled that Mozart grew fonder and fonder of Cäcilia and she of him. She described him rushing to their lodgings at the Golden Plough in Wieden, carrying coffee and sugar, and presenting them to Cäcilia saying "Here, mother dear, now you can have a little Jause."
After Fridolin Weber died in late 1779, Cäcilia relied partly on a 700-florin annual stipend that Joseph Lange agreed to pay when he married her daughter Aloysia on the 31st of October 1779. She also took in boarders to generate additional income.