score:5
My apologies, the first answer was applicable to MRT (subway) ... She is young enough for free child travel (until age 14), but too tall as 90 cm is the cut off height.
On the brightside, child fares on quite cheap starting at 8 baht. Bangkok Expressway And Metro (same basic rules for purple line)
For the Sky Train, they offer only Student Rabbit Cards (stored value cards), but normal fares for single tickets.