She can start the Holy Basil straight away. I have done some testing on Holy Basil supplements and the one I have recommended to a few clients is the New Chapter brand. It's very good. You can't OD on it ... so tell her, whenever she feels stressed, just pop a couple in her mouth ... and here's a good tip, instead of just swallowing, have her pop the capsules with her teeth and allow the liquid to remain in her mouth for a minute before swallowing.
I don't think there are any contraindications with Holy basil. It is food. A sacred plant with high frequency. And it is adaptogenic, so it works as needed.
Holy basil is also known as tulsi - she can also sip herbal tulsi tea as well as take the capsules.
A good adrenal support supplement may include: Siberian ginseng, licorice root and gota kola.
Also chromium is useful if she has some blood sugar problems causing mood swings - swings in energy will cause stress.
There isn't anything you or I have mentioned that can not be taken immediately. And they can all be taken together.
Bear in mind that herbs and vitamins are supportive of a stressful life but do not remove the cause of stress.
You have to look at the cause. What is causing the stress? Make sure she receives emotional therapy and perhaps some relaxation training (meditation, deep breathing etc.) and lots of love and attention to make her feel extra special. And buy her some soothing music to lie down with which can entrain a natural relaxation response.
Hugs to your mom