Hello, I'm Dr. Bob.
Many different condtions can cause bright yellow urine.
How long has it been this color?
Dog's urine may become yellower in color with increased concentration due to holding the urine longer in the body, to certain dyes in dog foods, as a result of the breakdown of red blood cells in the body, as well as a few other reasons.
If you look closely at the whites of her eyes, do you notice a yellowish tint to them?
Good! That would have been a serious sign.
If you know she's had to hjold her urine for some time before you see it's dark yello, this could be the result of simple concentration of the urine. If that is not the case, then changing her over to an all natural dog food may eliminate the dye that could be causing the color.
If she seems ill in any way, a urine specimen should be submitted to her veterinarian and she shoud receive a thorough physical examination to try to find the reason for this sign.
In most cases there is a non-serious cause to this symptom, but once in awhile, a disease process can be causing this sign to appear, and it should not be ignored.
If you should have further questions, please let me know.