Answered by Shaykh Faraz Rabbani
The sweater belongs to you, as your mother-in-law used your property without your permission.
`Ala’ al-Din al-Haskafi mentions in his Durr al-Mukhtar, a primary reference for sound positions in the Hanafi school:
“If someone purchased cotton and a woman knitted it, then the entire knitting is the owner’s.”
This was confirmed by Ibn Abidin in his Radd al-Muhtar, a supercommentary on the Durr, where he referenced the issue to the early Hanafi fatwa work al-Multaqat. [Ibn Abidin/Haskafi, Radd al-Muhtar `ala al-Durr al-Mukhtar, 4.219, Bulaq ed.]
And Allah alone gives success.
Wassalam,