As the owner of a 16 1/2 year old in a multi-cat household here is my opinion..

At Penny's age adjusting to a new, particularly young and energetic, kitten would be stressful for her. With Penny's advanced age she will soon, if she's not already, be experiencing the enevitable effects of aging; stiff joints, decreased hearing, & eyesight. Those things will make it more difficult for her to interact with an exuberant kitten.

My honest opinion is that Penny has had a good many years with her son, but now may be the best time for Penny to have all that love and attention to herself and to console her loss in her geriatric years. As her body gradually slows down, her health may require more medical attention/special foods, and she may have special needs as she ages, which would be difficult to accomodate if there is a kitten in the house also.