money on storecard for someone else

familyowes

Hi Newbie here. love your site. Have a huge problem.
About to marry this August. Lovely man hardworking and good with money.
Heres the problem his sister bought a cooker and hood from my argos account over two years ago. Since she has become an alcohlic mess refusing to work,- I now pay her argos account which ocurrs around 29% interest a month. She sits there drinkin. (got money for drink got no money for me!).
Anyway I aproched her tonight with my fiance (her brother) to get a load of abuse from her and told to (be polite) "get out of her house".
I know that we have a good credit rating and can obtain a interest free credit card for the bill, which we will probably do. - BUT is there a way out of this nghtmare and do we have any rights?
She spent the money on a cooker and hood which is clearly in her house.
We have interest payment now of nearly £20.00 a month and to be honest is dragging our wedding savings down, as this only pays £30 off her debt each month.
We are both credit worthy, and have never fell behind with any payments.
Please help with any legal advice for us to recover the money.
Pease, please help no where to turn.
Thanks for reading.
Kind regards
Emma