Yes, C++ will not let you convert T** to const T**. While you probably could use an explicit cast, the best solution is to change your conversion from vector<string> so that it outputs directly const char**.
You must actually have purposefully cast away the constness of const char* returned by string.c_str, so don't do that!
std::vector<std::string> strings { "one", "two", "three"};
std::vector<const char*> cstrings;
for (size_t i = 0; i < strings.size(); ++i)
cstrings.push_back(strings[i].c_str()); \\convert string to const char*
mwArray mstrings(cstrings.size(), cstrings.data()); \\cstrings.data() is const char**
