If a 69 year old female just lost weight - about 4 sizes- how do you get rid of the sagging skin?

Difficult. This becomes increasingly difficult with age. As we age we naturaly lose some of the elasticity in our skin. This really cannot be reacheived even with good skin care. Unfortunately, sometimes he only way to remove that skin is with plastic surgery.
Remove it. Yes the only practical way to remove it is called a dermolipectomy procedure.
Surgery. The only way to remove excess skin is with surgery. If you are healthy and a work up shows preoperative clearance you might be a candidate.
Removal. Unfortunately, nothing short of surgery to remove the excess skin is likely to work at this age. This may include facelift, tummytuck, etc. Depending on where the excess skin is located. Consult a board certified plastic surgeon.
Surgical excision. Only one way is known and that is surgical removal of the excess skin. Many areas can be treated, but not all at once. Typically, we begin with the area that bothers the patient the most, often the lower abdomen. Any board-certified plastic surgeon can help you.
By picking. An asps plastic surgeon & by following their recommendations/instructions to the letter. There truly are no other good options!
Surgery. There is no other way than surgery to get rid of excess skin. If you are in good health, there are numerous procedures that could help you.