Tax filing of wife of an nri living in india

Hi,

I am staying in US for the past 2 years. I am overstaying in US. Every month I am sending money to India into my savings account and my wife's savings account.

I am investing in Mutual fund through my wife. Currenlty I am investing 1.7 lac in Mutual fund through her per financial year. I am planning to open a DEMAT account and start buying shares worth around 5 lac. 

My questions are:

1. Is it necessary for her to file tax returns?

2. Is there any limit on the amount she can invest in Mutual fund and trading shares per year?

3. I will buy the shares but do not sell till 5 years? Do I still need to file ITR, as I am not selling them in the near future?

4. If I need to file ITR for her, how can I show the amount I am sending into her bank account from USA?

Please help me.

Thanks