Martin P-L writes:

Anne and Jane lived  together in Conduit St., Hanover Square, unmarried.  They both died at Lilford, Jane in 1782, aged 90, Anne in 1777.
An Anne Powys married a Thos. Harwood at Bitterley in 1723, but I do not know who she was.

EAP transcribed from Philip Powys' notebook: "Anne Powys my eldest Sister dyed at her house in Conduit Street. 22nd May 1747.

TFPL:
In the copy of Philip Powys' memorandum book it says that "Anne Powys my eldest sister dyed at her house in Conduit Street 22nd May 1747."
Anne was godmother to her nephew Thomas, second son of the same Philip Powys and Isabella Lybbe.
Her will survives.

In fact Sarah had been his eldest sister but had married when he, Philip, was about 6 and then died when he was about 23.  He probably saw nothing of her after the age of 6.  Certainly when Anne died, she was the eldest living sister.
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There is this christening of Ann in St Giles in the Fields, High St, Holburn in February 1690/1:

“18  Ann dau of Sr Thomas Powis Barr & Sarah his wife. Born ye 10th Inst”
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The burial register of Lilford parish church - thanks to Ancestry for this image - has this record:

“1747
“. . . .
“Mrs Anne Powys ye Daughter of ye late Sr Thomas Powys Kt was Buryed May 28 1747. Obiit 22 Aet: 56”
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Will of Ann Powys, Spinster of Saint George Hanover Square , Middlesex 19 June 1747 PROB 11/755

From the Northants FHS booklet of Mon Inscriptions for St John the Baptist, Thorpe Achurch, pub 2015:

On a black marble ledger stone:
“In memory of Mrs ANN POWYS, second daughter Sr. THOMAS POWYS, Knight, who died May 22d 1747 aged 56 and was a truly pious good woman.”
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