Absolutely- time to go to another vet. I can't imagine a vet not wanting to look into such a problem further after it had gone on for several weeks and nothing seemed to improve it. Diarrhea- and BLOOD in the vomit!- that has been going on this long needs to be taken seriously.
If a bland diet doesn't help the problem within 2-3 days, you can generally rule out an acute episode caused by something they'd eaten or some kind of food intolerance. There's an off chance your dog has an allergy or an inability to digest chicken….if both the bland diet & her normal food contain chicken it COULD be the culprit. Might be worth asking the vet....I believe there are allergy tests they can do that would indicate a food allergy? It isn't good to feed a bland diet for too long...it's not nutritionally complete for proper maintenance....and if it isn't working anyway, it's time to dig deeper.
I'd start with a fecal analysis to check for parasites (even if your vet's done it already it can't hurt to check again) and go from there. If you see blood in the vomit, bring a sample of the bloody vomit to the vet as well. Bloodwork would be the next step. Ivoss mentioned EPI, and I agree it's smart to check for it....it's definitely worth researching so that YOU know what questions you might want to ask the vet, here's a link:
If bloodwork was inconclusive I'd then want to do X-rays to rule out a tumor or something- which can also be a cause of blood in the vomit & digestive issues.
Only other thought, if he happens to be eating Blue Buffalo dog food….I recently had a problem with one of my dogs who suddenly had intermittent diarrhea. Ruled everything else out- a change in kibble fixed the problem overnight, so it had to be the food. The company confirmed they'd done a "minor" formula change that was supposed to make the food easier to digest. It apparently didn't sit too well with Jibini. I have not encountered any other owners with similar complaints, and my other dog ate it with no issues. It may have just been an isolated issue with my one dog, I feel Blue is still a good food....but I figured I'd mention it just in case.
Hope you get to the bottom of her problem soon. Let us know what you find out.