I have meniere's as well and stemetil really helps me.
I also take betahistines to help with my general ear problems and help prevent attacks and have a nasal spray.
Blood test may pick up on some kind of infection or possible other marker to show something causing the problem (quite a few problems which aren't necessarily ear related can cause vertigo eg inflammation following a virus, MS). For example, they may be able to pick up on a raised white blood cell count to suggest and infection or virus.
I saw ENT at first then neurology before being referred to a specialist neurologist in that area.
Had all kinds of tests done, the main ones being for ear pressure, calorics (reaction to water in the ears), flashing light tests and hearing tests as well as balance tests.
If she can recognise warning signs, that may help. I get a very sick feeling in my tummy then go into an ice cold sweat first so know when to get down and stay still.
The main thing is to reduce movement, get comfy with as low a bowl as possible for being sick without having to move the head more than needs be. Maybe a strong waterproof bag?
A blanket is good as it knackers you out so can be warm and just sleep after.
You can get stemetil in different forms such as suppository, ones which melt on the tongue and in inection forms which may them easier to take in an attack.
A low sodium diet is recommended for menieres, check on packets, even bottled water, for sodium content and avoid salt if possible.
Ginger is quite good for sickness eg ginger tea or with honey on toast or ginger biscuits.
She may be able to identify certain triggers such as moving or flashing lights (it can be related to migraines), movement in lifts or on escalators etc...