Hi Christina,
I'm sorry, I've been going round and round on this one, and all I've succeeded in doing is getting myself thoroughly confused.
I found the IGI entry, which is where I presume you got the baptism date, and tried to find a John Tonks marriage with a Mary Ann, with no success. There are virtually no Kettledons of the right era registered for anything!
Yes, on the face of it Emma could be Maria's aunt (nee Kettledon?) since both Maria and William (Emma's son) are said to be grandchildren of old Maria. Maria does seem to be a bit of an orphan, though, and it is possible there is a more complicated relationship than that.
Anyway, here are the (vaguely) relevant entries I have found. Sorry, I've lost the exact addresses - all in Walsall.
1861
Thos Whitehouse abt 1830 Walsall, Staffordshire, Head, wheelwright
Emma Whitehouse abt 1838 Walsall, Staffordshire, Wife
William Whitehouse abt 1860 Walsall, Staffordshire, Son
Maria Kettledon abt 1802 Brend, Staffordshire, Widow
Thos Kettledon abt 1840 Walsall, Staffordshire, Son, whip thong maker
Enoch Kettledon abt 1847 Walsall, Staffordshire, Son
Maria Tonks abt 1849 Walsall, Staffordshire, Granddaughter [of Maria, I would think]
1871
Maria Kettledon abt 1801 Brewood, Staffordshire, Head
Enock Kettledon abt 1848 Walsall, Staffordshire, Son
Thos Kettleton abt 1840 Walsall, Staffordshire, Son, whip thong maker
Henry Kettledon abt 1845 Walsall, Staffordshire, Head , whip thong maker
Maryann Kettledon abt 1845 Walsall, Staffordshire, Wife
Alfred Kettledon abt 1869 Walsall, Staffordshire, Son
1881
Upr Rushall St 5 Carvers Yard, Walsall Borough
Enoch Kettledon abt 1847 Walsall, Staffordshire, Son
Maria Kettledon abt 1802 Brewood Nr Wolverhampton, Head
Thomas Kettledon abt 1839 Walsall, Staffordshire, Son
William Whitehouse abt 1861 Walsall, Staffordshire, Grandson
Don't think I've been much help in the end!
Ros