Only way I see her ever getting her inventory slots up, is if they repeat this gacha multiple times, or make the bride version a part of other gachas. So far, I haven't seen a thing for increasing inventory slots other than exclusive dress blooms for specific girls. And the current gacha can only be played once, so even if someone wanted to spend $440 on going through this gacha 4 times, he can't.
Is Cactace Bride stuck wearing only a ring forever?
But, seriously, the 11k N-Gold is over the top. For that kind of dough, I'd expect a girl to have at least 4 inventory slots and 4 skillslots (since for skill slots, the generic skill blooms do exist, so it is technically possible to max her)
I'd even go as far as to suggest making the 6k N-Gold step-up cards have 2 inventory slots and 2 skillslots by default.