It may be that there was only one Cassandra and that the appearance of two is error on the part of the census enumerator.

1.  Marriage Record:

2.  1840 Census Index/Images (online at Ancestry.com, Image #15-16 of 24; extracted by Diana Gale Matthiesen):

1840

PA

Greene Co.

Whitely Twp.

Roll 461

pp. 86B-87A

Ln. 26

Elisha Rose

000 010 - 310 001

0100000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	20-29	1810-1820	= Elisha (b. 1812)
3 female	4 or under	1835-1840	= Elizabeth (b. 1837/8) = M. J. (b. 1835/6) = Sarah (b. 1835)
1 female	5-9	1830-1835	= Nancy (b. 1833/4)
1 female	30-39	1800-1810	= Elizabeth (b. 1808/9)
1	person employed in agriculture

3.  1850 Census Every-Name-Index/Images (online at Ancestry.com; Image #9 of 26):  Perry Twp., Greene Co., PA, Roll M432_783, p. 203A, 66/66, enumerated 11 Oct 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):

Elisha Rose	38	M		Farmer		Pa
Elizabett "	41	F				"
Nancy     "	16	F				"
Sarah     "	15	F				"
M J       "	14	F				"
Elizabett "	12	F				"
Susanna	9	F				"
Harriet   "	7	F				"
Casandra? "	2	F				"

4.  1860 Census Index/Images (online at Ancestry.com, Image #22-23 of 37):  Spraggs P.O., Wayne Twp., Greene Co., PA, Roll M653_1114, pp. 821-822, PN 205-206, 1423/1402, enumerated 10 Sep 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

Elisha Rose	47	M		Making wooden Boles?		100	Penna
Elis     "	50	F					"
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Sarah A Rose	22	F		Home Domestic			Penna
Elis J   "	17	F		Do     Do			"
Susan H  "	15	F		Do     Do			"
Harriet  "	13	F					"
Cassa    "	9	F					"
Jasper   "	7	M					"