How much, if any, of retirement savings can go toward purchasing real estate?

Hello! I’m 25 and not anywhere near retirement (shudder) but I’m trying to help my mom (65) by learning about retirement and helping her get a financial advisor.

She has roughly 2.5 mil saved in the market and she has always talked about having a retirement home on the water. I realize this is a huge oversimplification but I was wondering general advice on purchasing property/a home with retirement funds.

Is there a rule of thumb for how much to take/not take from savings? Is purchasing a home a good investment for my mom?

Thanks so much!