Equity Question Help

[Brittany King]

 Hello BP family! I hope you all are doing well. I'm seeking advice for a friend of mine. She's buying a house in AZ from someone she knows. The house has 125k in equity in it. The questions are 

1.how can my friend (the buyer) use the equity in the house to pay for a down payment and closing costs? 

My friend was given advice to only use 100k of the 125 

2 What happens to the 25k if she doesn't use it? 

3 Why should she not use the entire amount of equity if she can?

Thank you all for your time and advice. Have a great day.