"The girl puts on a white dress."
Translation:La niña se pone un vestido blanco.
Like this? [La niña ponerse un vestido blanco.] This sentence is wrong because it doesn't have a conjugated verb. Since the subject is the girl, the verb has to be conjugated in the 3rd person singular, the way it is in Duo's sentence.
You could use your ponerse if the sentence already had a conjugated verb first:
Ella va a ponerse un vestido. She is going to put on a dress.
Ella quiere ponerse un vestido. She wants to put on a dress.
Ella necesita ponerse un vestido. She needs to put on a dress.
Well I'd actually meant keeping poner conjugated to pone, and attaching the pronoun to the end of it, but it has since become apparent that I can't do that with a conjugated verb and I must put the pronoun in front. However, thank you for the response, it is informative and well stated.
It seems common sense to shower oneself. How would you say you are showering someone else in Spanish? In English, I would say 'the mother is bathing the baby'. (I may be wrong, but it sounds unnatural to say the mother is showering the baby - probably because a shower would shock the baby with the water falling into the eyes.)
Ponese isn't correct becuase of the verb form. This verb is conjugated to pone. The shift in word form occurs when you are using the base, non conjugated form of the verb, in this case, poner. If the sentence requires se poner, the se would move to the end of the verb, however that doesn't happen with conjugated forms such as pongo, pones, pone, ponen, ponemos. Now to tell if you need the base, or conjugated form of the verb, you have to check the sentence for a verb that has been conjugated already. @Marcy65Brown explained that part quite well up above. As a side note, we are just getting into it at this level, but command forms can have the pronoun shift as well, however that isn't relevant in this conversation.
I've found that it is helpful to break down a sentence by phrases: "La niña" is feminine, of course, so the whole sentence isn't masculine.
We are talking about a third person, so that is why "se pone" instead of "te pones" if I were talking to you, or "me pongo" if I were referring to myself. (No gender there, btw)
With "un vestido blanco" all three words are masculine to match the masculine vestido. And there is only one white dress, so all three words are singular.
Just something I've figured out and it works most of the time.