Your letter about your concerns about your sister raises many issues, some named and some not.
There is certainly such a thing as compulsive buying disorder - and it will be on a spectrum. Which of us hasn't cheered ourselves up by purchasing something glossy and new - whether it is a lipstick, a magazine or a car - and felt the better for it?
Dubbed "retail therapy", the science backs this feel good factor with a growing body of brain research, pointing to a chemical called dopamine. This chemical is associated with feelings of pleasure and satisfaction and it also plays a major role in drug use and other addictive behaviours.
Reading between the lines in your letter, however, I am getting the sense that your sister may be more in the category of the compulsive buyer rather than in than the retail therapy camp.
You make a comment about the unopened bags, which tends to indicate the situation is one of excitement of anticipation, (in this case, shopping), and of more significance than the end product. Once those shoes, that jacket, or the high thread count cotton sheet set has been bought, it can- for some- be almost a let down, says University of Kentucky's Dr Berns.
It is this link between anticipation of the experience and let down which makes me feel concerns for your sister. The cycle tends to follow a pattern where the let down builds until the need for pleasurable anticipation triggers the next bout of shopping.
You say your sister cares for your father - and is sweet and generous - suggesting that she is a giver and a non-complainer. How much do you know about how she is really feeling about her situation in life? Taking care of an invalid parent at the age of 35, harks back to a much earlier assumption of female family duty. There must be a sense for her of being out of step with her contemporaries? Is her sunny behaviour masking some degree of despair at a situation which possibly has no options, built in? Might she resent her role in the family? Could she be isolated, bored or frustrated? In other words, could this urge to shop be targeting a temporary respite from a low mood?
I can only make an educated guess here - and I might be wide of the mark - but certainly these are answers I would be seeking, regarding your sister's spending habits. Quite aside from the debt being raised, and the unwanted items, your sister may be struggling with poor mental health and 'coping' by relying on a shopping addiction.
In this age of "must haves" - when every shop window, advertisement and screen urges us to consume - shopping can range from a necessity to a pleasure, to a trap, to an obsession - and all stations in between.
There is no doubting the old adage that "a bit of what you fancy does you good" - but the lines are blurry and, as with any activity, keeping an eye on the thin line between controlling and being controlled is a good idea.
It is important that you talk gently with your sister about your concerns around how she is doing - and whether she feels it would help to talk to someone outside the family. Most people who use addictive behaviour to cope with their feelings are also very likely to be in some degree of denial. In our shopping crazed society, it is easy for the compulsive shopper to rationalise his or her activity as something everyone does. And of course it is - but it is a matter of degree.
Psychologist, Dr Engs of Indiana University has compiled a list of do's and don'ts to help people make better shopping decisions. These guidelines can apply to all of us at different stages of our lives.
The thrill of acquisition, followed by the dread of the arrival of the credit card bill is something most of us know. As with most things in life, it is about finding that elusive balance.
Use cash or debit cards where possible. Financial limits keep you from buying things you can't afford - despite the dopamine urging you on.
Window-shopping after hours can be pleasurable - without the risk of overspending.
Make a list of items you need in order to slow down impulse buying
Remember that the novelty of shopping when you are in a new place will put you at a higher risk of buying something you don't need - or really even want.
If you feel that you are out of control with your need to shop - then you probably are - and seeking help is a wise move.