17 yr old dachaund has breast cancer and is now drinking water excessively and urinating everywhere, could she also have diabetes and is she suffering?

I'd say she is suffering, to what extent I don't know, and as for what she might have, I don't know, but I'd say it's time to let her go now. Her cancer could even be everywhere. Do you want to put her through more tests? It's your decision, but I suspect that that will just prolong any pain.

She could be suffering from diabetes or from kidney failure (among other things). While neither are particularly painful conditions, they are not fun to live with - and if left alone may get worse and put her into a medical crisis.
You need to weigh your options here. Your dog is very old and has cancer - she now is most likely suffering from a separate disease that will most likely require extensive testing and medications.
I think you should sit down with your vet and discuss quality of life.