We have gifted plus dyslexia in a mainstream
private, doing fantastic with foreign language as highly verbal. It all depends on the resources you have available. A mainstream private cannot and will not teach your kid to read or have dyslexia specific expertise.
We have lots of resources so were able to do one on one OG tutor 4 hours a week for many many years. This was at least half of the high private tuition. It was a SLOG for time/energy/money but 1000% worth it. I avoided the dyslexia specific schools for my child because they are gifted and it would have been stifling. Also smaller classes for social development.
Good luck and never let others underestimate your child. But know the limits of what any one school can offer. If you go with Siena, just know the kid will need other social outlets, etc.