She pretends to be poor but spends like crazy?

My mother in law's husband is in corporate America and frequently brags about making 6 figures and live in a half a million dollar mansion. My husband says his mother hasnt worked a day in her life and needs to stop harping on him about education, etc. Anyways, when she and I go shopping she acts like everything is too expensive and she cant afford it. She harps on her son and I to be frugal, live below your means, and shop at bargain stores. One day she sent some clothes home in a shopping bag from a well-known/expensive home decor store. She had spent over $300 there on a quilt, sham, sheets, etc. My husband and I were appalled and felt she was a hypocrite at that point. Why does she harp on us but think its ok to do the exact opposite and fusses if we spent that kinda $?
Added (1). They have had 2 houses in 8 years of living here. They recently took on another mortgage and still owe several hundred thousand, plus put in a pricey pool/outdoor kitchen/theatre, etc.

Read more: She pretends to be poor but spends like crazy?