The 'Happy' star, who is a patron and trustee of the Essex sanctuary along with her manager Nicola Carson, is aiming to raise £100,000 by the end of the year.
Last month, both joined supporters to complete a sponsored walk, which raised over £14,000.
Hosting the most recent fundraiser, Lewis was joined by celebrity friends including Natasha Bedingfield and Glee's Matthew Morrison, who both performed for guests.
Hopefield managers Lianne Ingliss and Dave Schlaich (pictured above with Lewis and Carson) also attend the event, at which guests were treated to Lewis's specially designed cupcakes - made by a Puerto Rican lady flown in especially.
Other famous faces showing their support included Morrison's co-stars Dot Jones and Max Adler, Desperate Housewives actor Shawn Pyfrom, Teen Wolf favourite Colton Haynes, Perez Hilton, Dianne Warren, Jeremy Piven and Tyson Ritter of the All American Rejects.
Among the tracks Lewis performed were 'Bleeding Love', a cover of 'I'll Be There' and a duet of 'Somewhere Over the Rainbow' with Morrison - who previously teamed up with the singer on one of the London dates on her UK tour last year.
The 26-year-old returns to the UK later this week to host a Christmas Fete at Hopefield. Taking place this Sunday from 12pm, Lewis and former Sugababes star Keisha Buchanan will open the fair, while supporters will be entertained by magician Dynamo and Britain's Got Talent duo Stavros Flatley.
Watch Lewis and Morrison duet at the event below: