First off, boas can be a handful to hold. I wouldn't think that they would be the best bet for a snake to handle while walking around the house. However, there are many different types of boas and sizes. A smaller boa would be easier to handle than a larger one.
If she does decide to go with a boa, and she is into boa morphs, then she should stick with BCI. There are many different types of BCI boa morphs. There are also basically two types of BCIs, dwarf boas and common boas.
Common (Colombian) boas are the larger variety. They have the most morphs, and are the most common in the pet trade. Adults tend to average around eight feet for females and six feet for males. They are very muscular and strong.
Dwarf boas, on the other hand, are a little less common, and have fewer morphs; although, they do have some beautiful ones, IMO. Dwarfs average around five feet for females and three-and-a-half feet for males. Their size does vary based on their locale, however. Mexican boas tend to be the smallest form of BCI, while boas from the bottom part of Central American tend to be the largest.