Are all her lymph nodes enlarged? If only one or two, that could mean some sort of localized disease, but I think the most common causes of generalized lymph node enlargement are lymphoma and some tick borne diseases. Since you've already done the lymph node cytology, you might as well wait to see what those results are, but if it is inconclusive, you might consider having your vet run a tick panel (not just the in house snap test, but a full tick panel to the lab) to rule those possibilities out.
When my dog (who was 11, but my cousin has a dog just diagnosed with lymphoma who is only 5
) had lymphoma, she initially had swelling only in the inguinal nodes, then it progressed to all the others over time. Initially cytology samples weren't indicative of lymphoma, and my dog had a myriad of health issues that made me not want to sedate her to remove a piece of tissue for biopsy, so we did a tick panel (negative) just to cover all possibilities, and I ended up seeing an internal specialist who used ultrasound to visualize their needle aspirate attempts, and they were able to get samples to confirm that it was lymphoma. That said, for the vast majority of dogs, my vet is able to get confirmatory samples- I think my dog was just a weirdo, or maybe had lower cellularity in the nodes sampled at that time (her disease progressed slowly, she lived almost 9 months with no treatment after I first noticed the enlarged nodes).
I do know of a few dogs whose enlarged lymph nodes were caused by TBDs, rather than lymphoma, so IMO it's worth ruling out if the aspirate comes back negative for lymphoma and doesn't suggest any other possible cause.
My dog was sometimes picky prior to developing lymphoma, and didn't really get any worse in that respect until several months after being diagnosed, after which point she became increasingly picky. I don't remember her vomiting but it's been a while.
If all her peripheral lymph nodes are enlarged, you have to keep in mind that her internal LNs are probably enlarged as well, and that can cause problems due to pressure on the intestines and other organs.
Good luck with her. Fingers crossed for something that can be treated!