This is a complicated question, and the answer is not straightforward.
If the turkeys she had the chickens with were carriers of HVT (HerpesVirus of Turkeys), then the turkeys were likely shedding this virus. It could then be inhaled by the chickens, infecting them with HVT. This sounds scary, but it's a GOOD thing... this is essentially what a vaccination does.
HVT is MDV-3, meaning that turkey herpesvirus is Marek's disease, serotype 3. Serotype 3 Marek's cannot harm chickens, but it CAN give them an immune response and help them develop resistance to MDV-1, which is the scary kind of Marek's. MDV-1 is chicken Marek's, and is the kind that can kill them.
So essentially, yes, IF the turkeys were shedding the HVT, and IF the chickens became harmlessly infected with it at a young enough age, it sure can help to give them resistance!! Some people have success in controlling Marek's outbreaks by free ranging their chickens with their turkeys. It's not foolproof, but it does seem to help some people.
The only problem is that there are some unknowns with this method. Were the chicks exposed to the HVT before they were 36 hours old? This is the crucial window for proper immune system growth. Exposure after 36 hours old is still helpful, but not as important as the exposure within the first day or so of life. That's why Marek's vaccination is administered right at hatch.
Does she know if the turkeys are actively carrying HVT? If not, then there is no virus to shed, and nothing for the chickens to build immunity against.
You can vaccinate them now, but it may not help them. If they have already been exposed to Marek's, then it is thought that it won't help them. If they have not, it might help, but it is not the same as vaccination as day-old chicks.
I have some more in-depth information in my signature link if you'd like to read more!
