How to help Tuyet
Tuyet General Principles:
Target examples so Tuyet realizes that she has something to learn! (e.g. She incorrectly believes that 0.48 is larger than 0.84).
Teach underlying principles with concrete models (e.g. LAB).
Incorporate decimals of various lengths in the one situation wherever possible.
Conduct class or group discussions on this and other misconceptions.
Provide opportunities for Tuyet to use her new understandings.

What does Tuyet need to learn?
Tuyet knows there is a similarity between the patterns of column names on the right and the left of the ones column (although other students with reverse thinking may think the symmetry is around the decimal point instead giving a "ones column as well). She uses her place value knowledge "in reverse". She thinks the place value is the same on the left and right.

...., hundreds, tens, ones, tens, hundreds, thousands, ....

Tuyet needs to learn how to say and spell the place value column names and learn that the value of each column decreases to the right. Making decimal numbers using a model will help her.

Lesson Ideas:

LAB

Tuyet needs to make the correspondence between the physical size of the pieces and the part of the number which they represent. She must make the correspondence between the size of the number and the length of the LAB pieces or the volume of the MAB pieces.

with any model....

Stress that the size of the pieces associated with the place value columns get smaller as you move to the right.

Take care!

Be careful with pronunciation of tens and tenths ... Don't abbreviate: write & say names in full