If Anna Margarethe is telling the truth about her age, then she has to be Friedrich's second wife because she would be too young to be the mother of the older children.  My guess, however, is that she's fibbing about her age.

1.  Marriage Record:

2.  HADIS: Hessisches Archiv-Dokumentations-und Informations-System: Hessisches Staatsarchive Darmstadt (HStAD): Auswanderer-Nachweise (R 21 B) (online at www.hadis.hessen.de):

NACHWEIS Straub, Friedrich, Herkunft: Crainfeld. - Auswanderungsdatum: 1839-04 / Ziel: Amerika, USA. Quelle: Auswandererkartei Walter Möller 1839

NACHWEIS Straub, Friedrich, Herkunft: Crainfeld. - Auswanderungsdatum: 1839-04 / Ziel: Amerika, USA. Quelle: Auswandererkartei Walter Möller 1839

NACHWEIS Straub, Friedrich, Herkunft: Crainfeld. - Auswanderungsdatum: 1839-08-19 / Ziel: unbekannt. Quelle: G 15 Büdingen Q 34 1839 Nr. 11

NACHWEIS Straub, Friedrich, Herkunft: Crainfeld. - Auswanderungsdatum: 1839-08-19 / Ziel: unbekannt. Quelle: G 15 Büdingen Q 34 1839 Nr. 11 1839

Translations using Google language tool:  NACHWEIS = proof; Herkunft = origin; Auswanderungsdatum = emigration date; ziel = target; ubekannt = unknown; Quelle = source; Auswandererkartei = emigrants card. Büdingen is a town in Wetteraukreis, Darmstadt, Hesse.

One of the Friedrich STRAUBs appears to be our subject.  The other may be the Friederick STRAUB of Darmstadt and Pittsburg.

3.  Passenger Lists of Vessels Arriving at New Orleans, Louisiana, 1820-1902.  Micropublication M259-19, RG036, National Archives, Washington, DC (index and images online at Ancestry.com; Image #1 of 3):

Ship Kutusoff
Report and List of the Passengers taken on board at the Port of Bremer Haven whereof Edw E Taylor is Master burthen four hundred & fifteen 45/95 Tons and bound from the Port of Bremer Haven for New Orleans [arrived 11 Dec 1839]
Names	Age	Sex	Country to which they belong	Country Intending to Inhabit	Occupation	Bagage and Remarks
5. Friedrich Straub	49	Male	Crainfeld	St Louis	Farmer	5 Chests a/ Cloaths, Houshold, Furniture, Farming utentials, Bedding
6. Anna Marg: Straub	38	Fe Do	do	"
7. Heinrich Straub	23	Male	do	"	Schoemaker
8. Friedrich Wilh: Straub	20	Do	do	"
9. Christoph Straub	18	Do	do	"
10. Anna Magar Straub	25	Fe Do	do	"
11. Chatharina Straub	20	Fe Do	do	"
12. Gretgen Straub	15	Fe Do	do	"

Anna Marg: might be 58, instead of 38. 

4.  1840 Census Index/Images (online at Ancestry.com):  can't find.

5.  1850 Census Index/Images (online at Ancestry.com):  can't find.

6.  Messages posted to the Straub Family Genealogy Forum (online at GenForum.com).