U.S. States: Texas: Grayson County
I would check KY 1850 census index, and see if there are any Hickman families in Lincoln Co, KY. Then check and see if they have a boy about 11 years old, named Henry. Common migration for families was from KY to MO, so Margaret and Henry could have married in MO. If nothing else works out, you could check every Lowery family in the MO 1850 census, looking for one with Margaret about 3 years old. I did every Burnett family in 1860 and found the family I wanted. I know it takes time, but worth it if you can find your family. If you decide on this route and find the family, I would then check marriage records in that county, for possible marriage of Margaret and Henry.
Since Blanco Co. is next to Travis Co. (Austin in Travis Co.), I would check out Blanco Co, TX GenWeb site, some GenWeb counties have their local cemeteries online. Hyperlink at the end of this message will take you to Texas GenWeb site, scroll down to county options. If you haven't visited the TX GenWeb site before, click on the many options, you may not need the info now, but will know where to find it when you do.