You say she is 17yrs old ??? my goodness.At her age things like bleeding from vagina could be rather sinister ! poor old darling....... Ginger is right get her to the vet as soon as possible and give her all the love and support you can.
I know little dogs get to this age and older but..... a bigger dog that is very rare what is your secret for helping her get to 119 dog yrs.
Hope she got a letter from the Queen lol.
Please let us know how this grand old lady is going.
This could be bleeding from her bladder. A possible cause could be polyps or bladder stones, or even a very bad urinary tract infection.
Otherwise, there is a possibility it is "stump pyometra" (what has been left behind of the edges of womb tissue after spaying becoming infected) However this is not all that common. My guess would be she has a bladder problem.
Please take her to the vet a.s.a.p. I hope it is something which can be easily remedied (say a course of antibiotics)
Let us know how she is, if you can.