I went through this, constant spending and chasing happiness when buying stuff, that lasts 2 minutes and im a debbie downer again. I get manic and need things straight away to get that bit of happiness. Ive got into major debt because of it. Turned it around last year. Realised I was lonely, depressed and had severe anxiety. Also have pmdd and I was getting like this during certain points in my cycle. Sorted myself out and realised that these material things were just material things that I didnt need. Im paying of my debt and even have some money in savings. If I see something I do want or do need, I save to buy it now. She sounds very similar to me and needs to get help before she lands herself into so much debt and her mental health with suffer as a result.