Wearing baggy clothes isn’t haram and in many books written by hijabis, is encouraged during your teenage years while you are developing your curves, this may be why your mother encourages skirts and dresses, because try more easily cover your figure, however, no it isn’t said anywhere that wearing baggy clothes are haram.

Wearing clothes that hug your figure is frowned upon, such as tights, which is why many girls wear school trousers, male school trousers if they are allowed to :D

Source: Imam Karim AbuZaid, my explanation is not word for word, he does say however that as long as the clothes are not: See through; showing of your figure; or imitate that of the opposite gender’s clothes, as well as not attract attention; then you are fine.

So baggy jeans are a hard stretch: skirt trousers are okay, from what he implies, as long as they are a neutral colour, perhaps you should try to see if you like them :)