It is possible to see all recent public posts (well actually all posts) in one's profile but simply attaching them to other profile doesn't go, at least not as imagined. Also, if you'd copy one post from one profile to another they wouldn't be where they are because merging of two profiles are not possible. Well technically I believe it would be possible one (complicated) way or another (also complicated), but I don't believe it worths to put so much effort into merging two profiles in deed.
The thing you suggest is actually not neccessary either as @elizabeth_jane said she'd just post with newer profile from now on and not that she'd delete the old one what means the posts are still there for all (including her) to see and read and as her older profile is still there she'd get the notification about possible replies to the posts too and according to deceision she'd answer with the profile she tends to use from now on.
Much more simpler than merging the profiles, deleting them or moving the posts from one to another I believe.
Hope it helps.