The French usually say "Elle a de longues jambes" - rather than "ses jambes sont longues"
but that makes no sense, why not "des" then? Why use de with plurals?
Unfortunately seven years later, still not accepted ..22 Feb 2020.
That's because it's not accurate translation of the sentence. "She has long legs" and "Her legs are long" may mean the same, but the grammar is different.
Probably, but 'ses jambes sont longues' is an odd way to describe a person's legs. This sentence is not good French.
Her arms are wicked and her legs are long, when she moves my head screams out this song, Hello !
Thought 'son' could be M or F ?
Provided the object possessed is masculine and singular, yes: son pied, son cou, son genou = his/her/its foot/neck/knee
But "jambes" is feminine and plural, so you need "ses jambes" : his/her/its legs.
I had "Elle a les jambes longues" but this was rejected. Why?
Or "elle a de longues jambes", both should be accepted (elle a les yeux bleus = ses yeux sont bleus...). This is the most common formula to describe a person.
If we say "Ses jambes sont longues", there is not any indication that the subject of the sentence is female, right? It can be translated into English as both "Her legs are long" or "His legs are long," I guess?
even its legs, for an animal for example ?
Can "Ses jambes sont longues" be translated as "Its legs are long" to indicate the legs of an animal?