First, that's called a
glottal stop and it is a common variant of T, especially in the middle of words, mostly in British dialects.
https://englishpronunciationroadmap.com/what-is-a-glottal-stop/(A similar feature of American English is the "flapping" of T in the middle of words like "water" being pronounced something like a quicker version of "wadder". That's just another kind of
lenition = weakening.)
Second, you should start by taking a step back and rethinking how you conceptualize dialectal variation. There's no "right" way to speak. There are
different ways to speak, and you might have one that you prefer, which is probably just how you grew up speaking (or how you were told you "should" speak by someone else who was told they "should" speak that way, and the cycle continues). But variation and change are natural parts of languages, and you should not consider someone who speaks
differently to be speaking worse (or "immature and unprofessional").
On the other hand, there really are some social stigmas out there (because most people buy into the myth that there are "right" ways to speak, because of existing social standards and prejudices, which end up boiling down to associations with people from certain regions, or just
other people). So there in some situations having a certain accent can be
perceived as, for example, unprofessional, and because people have that perception (it's really their problem, not that of the speaker), it could be harder to get a job, etc. But I would say that most of the time these concerns are exaggerated, and especially in the globalized world today there's so much variation that I at least hope everyone can be taken seriously regardless of where they come from. Still, it's a complex issue. Take, for example, the "Valley Girl" accent of some people from part of California, which very clearly represents an
identity (that's what accents are!), but can also result in the person not being taken seriously by others
because of that identity. In some ways, then, accents are like clothing, and people do get judged for how they sound or what they wear. But accents aren't something you can just put on or take off. (In that sense, these issues fall somewhere between judging someone for their fashion choices, and judging them based on race or national origin, although often much smaller groups than by 'race' or country.) Everyone has an accent. It just happens to be the case that some accents are
considered normal (what you might expect on TV, or from someone from your hometown), while others are considered less prestigious, less educated, etc.
So what does all of this mean? Well, if your daughter is talking like other people around her, that's
completely normal, and not something you need to "fix", and also probably not something you can control. If she is speaking like that outside of an area where it is common, maybe because she's copying movies she likes or something like that, then it might cause some confusion or lack of closeness with her peer group. But in the end, peer groups in adolescence are one of the strongest factors in shaping an accent (more than parents), so that will probably sort itself out. Regardless, one of the worst things you can do is try to control how she speaks or make her self-conscious about it.
In the end, the only constant in language is change: "would you look at how the kids these days are talking..." has been said for centuries.
