Since all of us are endowed by our Creator with different gifts and talents, for our personal use as we are willing to account to HIM for ... embrace the differences and celebrate the fact that none of us has been struck down yet.
Surely, your SIL spends money on things that you wouldn't, or could care less about having. And, I can fairly well guess that when she acquired her "things" she didn't always use her best economical judgment (which is probably not something you need to point out to her <g>).
Her advice about using wisdom with when, where, and how you spend your money is valid, but only so far as "it is always good to use your resources wisely" ... and, you can thank her for reminding you (if you want to) ...
example: I had a SIL who had furniture and home improvements that I could never afford, nor would I have ever chosen to spend my money in that way. She didn't like the way I ran my house or what I didn't have compared to her - - but, guess who had the money for them to come to visit when they needed gas money, and a bunch of other gifts???
we always have a choice - - we can be angry for forever, or we can take the advice we need to use and forget the rest of it.
Life is too short to try to get even, but it is long enough for each of us to learn to appreciate the differences we find in our families. Those differences all have a purpose - - if to only knock off our rough edges.
I know for a fact that a lot of people have no appreciation for my ability to knit, crochet, sew, and quilt (or write <g>), but then, I am not too impressed with all the horses or makeup or diet plans they involve themselves with, either, so maybe it breaks out even somewhere down the road.
One other thing - - you might spend more time talking about the weather when you are around this person - - she doesn't sound like she has learned manners, yet - - best to leave that to some other hearty soul, eh? <wave>