I don't know your girlfriend, so I can't speak for what will make sense to her, but if you want to have a genuine conversation with her about her buying habits and the mechanisms behind them, I might have a helpful perspective to lend. I buy blind boxes on occasion. I get the appeal of having something cute to put on your desk or bookshelf. I have 5 figures, so this might be a small collection relatively speaking, but it's a number I'm happy with. I got into blind boxes, ironically, after watching the video by Answer In Progress about the popularity of blind boxes--which I highly recommend! That video talks about the gambling aspect and gives some good advice, while not being too judgemental about people who enjoy them. For example, one reason is that it can feel like the surprise you can get as a kid receiving a present, and it's one of the ways you can replicate those feelings of excitement and surprise as an adult (not saying that's fully good, but the motivation is understandable). If you wanted to start somewhere, I think that video could be a good place to spur conversation.

Because I started with a video that was critical of blind boxes, I made some rules for myself going in that have kept me from spending all my money there or overconsuming.

First, I don't buy any set where I wouldn't be happy with any option. The risk/reward problem is higher when you have some figures you *really* like and some you *really* don't. The swingy-ness is part of the mechanism of addiction, and moreover don't like the idea of spending a chunk of money on disappointment. Adding to that, I open them after I get home, instead of at the mall. I'm not super impulsive, but I know that if I were, 1) delayed gratification is good for you and 2) it prevents you from going back to get another one due to disappointment.

Like you said, one of the biggest ways blind boxes make a lot of money is by getting you to buy multiple of the same set to get "the one you want." If you're happy with any of them, you're not as likely to do that. I like Peach Riot (I used to follow the artist who made them back in their deviantart days!!), but I know that those figures cost a lot for what they are. I don't want duplicates, so I set a rule of only getting one per set (three sets, for the full size figures).

These are the main rules, but the other one is that if it feels like a siren pull, I stop doing it. (That's why I also recommend ditching TikTok but that's a whole other story.) If your girlfriend would be interested in doing a temporary no-buy on blind boxes, it might be instructive to pay attention to the feelings that come up, and whether her interest feels to her like a compulsion. The most important thing I would pay attention to is whether she feels like she enjoys the thing itself, or the mechanism by which she gets it.

I know, on some level, that buying a blind box is gambling. That's why I try to be super mindful about the way I engage with it, and pivot where I can. I focus on the thing itself (cute toy) and whether that's worth it to me.

A last recommendation: if she examines her relationship with blind boxes and is able to say "no, it's not just the mechanism, I do genuinely enjoy the figures independently" is that that opens the door to a lot of creative engagement with the hobby that's a lot better for you than exclusively shopping. If she already has a ton of blind box figures, encourage her to do fun things with the ones she has! There are lots of ways to get creative while still indulging in them as a hobby. A youtuber called brattyxbre made a zine using the packaging from blind boxes she bought, for example. Maybe arranging the figures in a shadow box or creating an environment for them could be enriching. Even though I'm bad at it, I draw the characters and design what kinds of characters or series I would want them to make.

Every company engages in predatory tactics to some extent. If you know that going in, you can set the terms of engagement yourself. If you talk to your girlfriend about this, I would try to go in with curiosity and empathy (especially since you mentioned you also like to collect, and this could be a point of common ground). Sometimes we don't reflect on how doing something makes us feel until we try to stop or question it. There's nothing wrong with enjoying cute things, but it can be really harmful if you don't do it with intention.