There can be a variety of reasons why your client's eyelashes are falling out. Here are some possible causes:

1. Poor Diet: Poor diet can lead to eyelash loss. A balanced diet rich in proteins, vitamins and minerals is important for healthy eyelashes.
2. Irritation from cosmetics: Using cosmetics like mascara and false eyelashes can irritate eyelashes and lead to eyelash loss.
3. Allergic Reaction: An allergic reaction to cosmetics or adhesives can also cause eyelash loss.
4. Age: Over time, eyelashes can thin and fall out. This is a natural process of aging.
5. Hormonal changes: Pregnancy, menopause or hormonal imbalances can also lead to eyelash loss.
6. Friction: Friction of the eyes or face can cause eyelash loss.
7. Medications: Certain medications, such as chemotherapy or antidepressants, can cause eyelash loss.

If you find your client's eyelashes are falling out, you should recommend that they see a doctor to find out the cause. In the meantime, you should advise her to avoid cosmetics that can irritate eyelashes and be gentle with her eyes. A good diet and healthy lifestyle can also help prevent eyelash loss.

As an eyelash stylist, you should also ensure that you work with quality products and offer your clients comprehensive advice and care guidance to keep their eyelashes healthy and strong.