There are lots of good suggestions above. Mine is to reach out to the Portuguese Embassy. We're so lucky to live in/near the Nation's Capital and this is a great way to take advantage of it because of your proximity to the embassy. Now that things are opening back up they may resume with some events open to the public. Additionally you may find the language resources you want with them - either in a formal way through some of their programs or an informal way with a staff member who is willing to "tutor" your child or meet/interact for Portuguese speaking/writing opportunities.

Is there a Portuguese weekend school in the area? Generally that's the choice international families make, OP. We send our kids to the French weekend school, and know people who send their kids to the Japanese, Argentine and German weekend schools.

If you are in touch with other Portuguese families, and there is no school yet, you could get a group together, and start one, informally or formally. One of the Portuguese parents could lead a group, or you could find a formally trained instructor. This is how the French school came about.

In addition to this, we watch the news and movies in French, make them read French literature, and try as much as we can to speak in French (although they revert to English when they're together). The one thing we can't do is make them progress in the French essay-writing style - they don't have quite that level of competence, which means they would struggle in French high school and to pass their Baccalaureat (end of high school exam), which is very writing-heavy. Thankfully, they're targeting English-speaking universities.

iTalki has lots pf people who just want to talk. Yes, they charge, but its really nominal.

Social media. As a teenager, you'll definitely want to supervise her from a distance, but social media is a great way to find "pen pals" to Skype or FaceTime with in a foreign language. Professionals will want to be paid, of course, but other teenagers in Lisbon or Rio or wherever (acknowledging those are two different dialects) might be eager to bond over a common interest (music, sports, etc).

Travel, university/classes and foreign films. Where there Be Dragons has some foreign language options but I don't remember what they are.

I reached the point where I wasn't progressing anymore and was discussing with an aunt who taught the university level of that language. You need live people to speak with. I tagged along on her study abroad courses. The local university also had immersion options, too.

Spoke Portuguese as a child and always spoke to child in Portuguese. She went to a daily mother tongue class and was up on her reading and writing in Portuguese. Now that she’s starting high school we need to continue on weekends with a tutor (maybe?) or some other way to keep her improving beyond me.

How do others do it?