Good on your daughter!
I started learning Esperanto from Duolingo a couple of years ago.
In my opinion it's probably the only language - due to its simplicity - that you actually can learn properly via Duolingo.
Having finished the course I fairly gingerly went along to an Esperanto meet up (that I was amazed to learn it had actually been occurring regularly within walking distance of where I lived), and was surprised by
(a) the fact that I could actually use it to communicate after learning what was really only about a year
(b) how friendly and encouraging the people were (to tell the truth, I was actually expecting zealots and/or weirdos)
(c) how many people are actually around who speak it. Meet ups can vary between 3 to 50 or so people and the form of those meet ups varies from simply chatting, eating out, a group that is into giving lectures on various things, a walking and cycling group, and a group that plays board games
(d) how varied the backgrounds are of the people I meet there. I've met people that I just would never have met otherwise, such as a former ambassador, a psychiatrist, a retired forester, etc.
(e) the opportunity to chat with people who I really wouldn't have been talk to otherwise. Esperanto is quite popular in quite a few countries where English is not the default second language or, if it is, people don't usually learn it to a level where they can converse. So I've met people from Poland who are of an age where only Russian was the second language one learnt at school, people from Cuba, Korea, Brazil, and so on.
In addition to that, there are a lot of free resources on the Internet, from a language course called Lernu that has more grammar explanations than Duolingo, as well as articles, books, etc. All free.
And if one is into travel, there is long-standing scheme allowing one to organise stays in other Esperanto speakers' homes for free.
In addition it's pretty standard to arrange to meet up with Esperanto speaking locals in other countries where they will show you around their city for free if that is what you're interested in.
Sorry, I'll get off my soap box now.