I have lost all fluency in Japanese. Japanese culture had always been a part of my life as a child, but despite my family (cousins, etc) growing up on misoshiru and jpop and anime, we all spoke portuguese, so Japanese-the-language never felt like "home".
These days, I also occasionally forget portuguese vocabulary. I do still "speak" with family, but mostly by text via WhatsApp, and conversations are usually pretty casual and don't involve nearly as much eloquence as, say, a good book. The vast majority of my life now revolves around english-speaking culture: my job is full of english technical jargon that I've no idea how to translate, english is the language I share w/ my wife, and it's the language I use to consume information and entertainment. English is now my "home", so to speak.
I think the author has a similar experience: she learned english in primary school and lived a primarily english-oriented life, so english became "home". The phenomenon of wanting to reconnect with one's roots later in life doesn't strike me as particularly unusual either. In retrospect, I did unintentionally distance myself from my own parents during my 20s (partly because that's sorta the whole point of becoming an independent adult and discovering new things) and only really started to regain that level of touch after having kids.
My point is: loss of language can have a lot to do with prioritizing things one feels are impactful in their lives (though those things may not necessarily be important - parents are certainly important, but it's the sort of thing that one can easily take for granted). Having had such a weird life experience wrt "first language", I'm keenly aware that the first-ness or even the familial aspect don't necessarily correlate with the cultural surface area that a person interfaces with the most. In some rare cases, your second - or third - language is what feels like home.