Heaven was very insistent that Alex isn't anything like as "dumb" as she comes across...
Well......she'd know
TBF, I think she'd had a lot of long chats with Alex, and there have been a lot of hints into Alex's background if you listen carefully for them, e.g. her charity work in Africa. For an 18-year-old, she's already done a heck of a lot with her life.
One of the examples that Heaven cited (and seemed very impressed with) was that Alex knew how to deliver a baby (I wasn't clear if that was from her charity work). Not all that unusual, perhaps, but how many 18-year-olds would you trust as a midwife?