That could very well be true. By 1851 she would have been around 40 & not so likely to have more children. As far as I can tell, she only had 2 during her 16 year marriage to her first husband, so she perhaps wasn't one of the more fertile women of that time!
By googling I think I've found that the Coldstream Guards were at St George's barracks, which is the same regiment as Elizabeth's first husband.