What's the name of Sylvia's Mother?

Mrs Avery

http://www.sylviasmother.com/lyrics/first/sylviasmother.htm

Her 'real' name was Louisa Pandolfi... Here's a link:

https://en.wikipedia.org/wiki/Sylvia%27s_Mother

"Sylvia's Mother" is autobiographical, with songwriter Shel Silverstein drawing upon his unsuccessful attempt to revive a failed relationship. Silverstein had been in love with a woman named Sylvia Pandolfi, but she would later be engaged to another man. Desperate to continue the relationship, Silverstein called Pandolfi's mother, Louisa, but she instead told him that the love had ended."