<human>: Condense the text into a few key points

I'm 21 and my sister is 33.  She's married with two young kids.  Growing up she was a great role model (long blonde hair, blue eyes, tan, in shape, ate well, etc).  We used to be able to swap clothes and shop together.  She's gotten significantly heavier, to an unhealthy point.  I've never been stick thin myself, but I worry about her.  Two kids and [PCOS] can only be a crutch to an extent.

I've lost a large amount of weight and her health is declining.  She's got a very sensitive personality and conveying that I'm a smaller size in a gentle manner is nearly impossible.  How should I handle the issue?  I'm not trying to rub my weight loss in her face, but it gets awkward when she's bought a skirt she doesn't like anymore and wants to give it to me.
<bot>: My sister and I used to be the same body size, but she has gained weight, and I've lost weight.  How do I handle our size differences without being a complete jerk?