even in TPM padme is set up as a replacement for Shmi. when anakin is 'cold' on the ride to coruscant, and padme gives him a blanket, padme is acting in the role of his mother. eventualy, anakin will transfer ALL his "Attachment" for Shmi onto padme. and this will explain the 'too-fast' love story. apparantly, to GL's mind, this ONE scene is enough to establish the connection: anakin uses padme to replace his mother. after this ONE scene, the only relevant bearing on the plot will only come after shmi dies. so really, that's ALL shmi has left to do, in order to fulfill her dramatic purpose: all that's needed from her now, is her death scene. "Freeing" her is not germane to the plot. in fact "freeing" her would actually complicate matters of storytelling... it is FAR more convenient storytelling to just say "watto wouldn't have it" and let her remain in jeopardy SO THAT she can die on tattooine in the next movie, AND fulfill her dramatic purpose.
--> I've said it before, Shmi should have been rescued at the end of TPM (by 'Qui-gons Defiance'), and they could set her up in an apartment on coruscant. the jedi could kidnap her, and take her away from watto.. and there would still be a price on her head (so she's still technically in 'jeopardy'). anakin would (secretly) visit her on coruscant for the next ten years, even though he's technically not allowed to have this 'attachment' by the jedi order. and the price on her head could be so small, that NO bounty hunter would bother to collect it, for 10 years... UNTIL..
until there is a price placed on padme's head as well, for being opposed to the military creation act: now the bounty hunter comes to coruscant to hit two birds with one stone: Shmi is killed on coruscant by jango fett in the opening scene of AOTC and the bounty hunter turns his sights onto padme now. anakin absolutely freaks out, and swears to protect padme, in ways he could not protect his mother. --> now he's transferring his feelings for his mother, onto padme - explicitly. Shmi still dies in AOTC (thus fulfilling her dramatic purpose). and anakin still swears to save padme from the same fate. granted: its not quite as 'convenient', but it makes more sense, and achieves the same dramatic purpose
--> anakin replaces his mother with padme and transfers ALL of his 'attachment' onto HER now. this explains the too-fast love story, from anakin's POV.
meanwhile, from padme's POV, "you'll always be that little boy I knew on tattooine". (padme's choice to enter politics has prevented her from having a family like her sister did -- she has maternal instincts, which she transfers onto 'that little boy from tattoone', and this allows her to 'love' him despite his faults, which include murdering an entire village - she forgives him, as a mother would).