Our subjects are living among a group of SIASes in the 1850 Census (see table), so I believe "Sally" is the Sarah SIAS said to have married a George W. SMITH.  The Sarah said to have married George W. SMITH is also said to be the daughter of Charles SIAS, Sr., but our subject is too young to be Charles Sr.'s daughter (unless Charles Sr.'s first wife died and he took a young wife late in life, for which there is no evidence).  The most likely alternative, assuming someone has accidentally attached Sarah to the wrong Charles, would seem to be that our subject might be the daughter of Charles, Jr., (from whom she is living just two doors down in 1850), but this seems impossible if his marriage date of 1808 is correct.  In the 1850 Census, she is living four doors down from James & Patience (DWIER) SIAS, whose children are not well known (i.e., most are unaccounted for), but more significantly, in 1840, she and George are on the same page of the Coventry census with James & Patience, and they are the only SIASes in Coventry.  In the 1830 Census, George & Salley and James & Patience are in Derby, Orleans Co., VT.  It seems extremely likely to me that Sally is the daughter of James & Patience. 

1.  Census Index:  U.S. Selected Counties, 1820 (Broderbund CD-314):  not found, as expected.

2.  Census Index:  U.S. Selected Counties, 1830 (Broderbund CD-315):

1830

Smith, George W.

VT

Orleans Co.

Derby

p. 201

James & Patience (DWIER) SIAS are also in Derby, but on p. 199.

3.  Census Index:  U.S. Selected Counties, 1840 (Broderbund CD-316):

1840

Smith, George W.

VT

Orleans Co.

Coventry

p. 359

On the same page with James & Patience (DWIER) SIAS, who are the only SIASes in Coventry.

4.  1850 Census Index/Microfilm (online at GenealogyLibrary.com):  Newport, Orleans Co., VT, p. 134A, 91/91, enumerated 29 Jul 1850 (Diana Gale Matthiesen):¤

Geo Smith	44	M	Farmer	950	Vt
Sally	44	F			Vt
John	22	M	Farmer		Vt
Roxanna	20	F			Vt
Lydia	19	F			Vt
Sophia	15	F			Vt
Edwin	12	M			Vt