<human>: Can you condense the text into three sentences or less?

She's been complaining about her slow notebook with a half-broken screen for the past half a year and she's been wanting to get a new one. She couldn't afford it and neither can her parents, so she's just been keeping it — and _joking_ that I should buy her a replacement.

I'm well off and figured that I could actually buy her one, so I did, thinking that I could get part of the expense back by selling her broken computer (probably worth 1/6 of what I paid). No big deal, we sort of did the same thing when I sold her my old phone for spare change in exchange for her old (again, broken, unsold) phone.

I got it yesterday, I spent the past 2 days searching for it and now preparing it for her. Today when she got home she was saying something like _"With the money I make by selling the computer…"_ which I interrupted by saying that I'd keep the money for that, lighted-heartedly adding _"What, you want your cake and eat it too?"_

That upset her and she grumbled about it until I asked what was wrong.  She told me she was mad at me because I _expected_ to get the computer without telling her first, that a gift is a gift, and that I shouldn't expect anything after giving one. She said that if I asked it wouldn't have been a problem. The "discussion" ended with her saying that I should take it back and sell it. I got back to the computer and she went out.

So here I am.

Was I wrong to assume that I could get some money back by selling it? I need some perspective.

Background: 18 months together, 1 month living in the same house — plus we technically already lived together temporarily for 2 weeks + 5 weeks, abroad.
<bot>: the day after I bought my girlfriend a new computer, she got mad at me for assuming that I would sell her old/broken computer and keep the money, hence technically _replacing it._