Drano is very toxic to your dog and can cause seizures and death if left untreated. You will want to take your dog to your nearest Vet ER center immediately. They will want to begin treatment immediately. I would not recommend inducing vomiting at this time as this is a acid based cleaner and can cause more harm coming up as well as if he aspirates it.
Please do not delay in getting him to a vet asap.
Even if she appears fine she still needs to go in for treatment. While she may be ok, it is not worth the risk in the long run should she take a turn for the worst.
They may want too induce vomiting with charchole.....with her being at the vets office already they can be prepared if she aspirates or has any problems. They may also choose to simply watch her and administer medications and IV fluids. If she has any issues such as seizures they can treat her immediately without having to wait for you to bring her back in.
I understand your concerns, she may be OK. But the fact is this medication is very toxic and the recommendation is immediate treatment by your vet. Regardless of how she is acting or how long ago it was ingested.