I’m for obtaining DNA in secret when the child visits you. If the results say she is not your granddaughter, you can end the relationship without getting invested emotionally only to be hurt again later on. also, as time passes, the child could be hurt as well, unless you are willing to turn A blind eye and accept her regardless. If the DNA concludes she is yours, hooray. Say nothing about the test to anyone. Keep it between yourselves. I don’t like to be sneaky, but this is simply investigating without hurting feelings, so the end justifies the means.