Since I come from H!P fandom I'm used to seeing kids work as idols, however, it's very different in Japan compared to Korea. For instance, in Japan nobody under 18 is allowed to work after 9PM. They still get to have free time, family time and go to school.
And then, meet T-ara who may only get 3h of sleep at night, may spend months without an opportunity to meet their family, whom fans send food to because they know the girls might otherwise go hungry (I know other kpop groups get this as well, but I believe my point still stands lol). How does throwing such a young girl into the mix work?
The sexualization would be a problem even if T-ara never performed a sexy song ever again and dressed up as nuns. Because in any case, they are putting this girl up on the stage to be ogled at, and that's going to attract a certain type of male fans (in addition to more normal fans). What she does, what she wears doesn't matter. It's like how pedophiles convince themselves that children are trying to seduce them (when in reality they are just acting normally). When you put a girl on stage, she will become the target of this kind of attention no matter what. It's kind of the burden of being female. However, not everyone has to or will read it or view it this way. Some casual fans might not notice anything strange about her presence. Perhaps she will be able to blend in with her height alone, as long as she's not given any questionable dancing solos lol. I don't want to judge the performances with her until I see how it looks. Ugh I guess, TL;DR Dani being added to the group would be problematic no matter what, but it doesn't have to ruin everything for everyone...? LOL