I send my child to a school in the local language--I am a permanent resident, but I know some other 100% foreign non-permanent families who also choose to do the same.
Choosing as an expat to send your kid to school in the local vernacular can be a wonderful choice, but it can also involve a lot of hard work and sacrifices.
Your child has to comfortable with it for a start, esp if they are over age 6 or so and there will be some significant catching up to do.
Language barriers can compound the psychological difficulties of moving home and having to make new friends, and this can be extremely stressful for some children.
Parents will have to manage school in another language, deal with significant cultural difference and communication issues, and also do extra work to keep their kids up with English, especially if they are going to be facing a competitive educational environment upon returning to the home country (the OP mentioned prep school so I am guessing she wants her child to use a private or grammar secondary school, which will involve passing tests).
In short, this can be a wonderful choice but it is perfectly valid for parents to say that they do not want this and that they prefer international schooling. It is not necessarily about being a snob or wanting to stay in an expat bubble.
The OP should try to get a grasp on how long she will be in the country if she can--if a short stay turns into a very long one, local school might be the better option.