I've bought my wife clothes.. I tend to check the size of her most current attire & go from that.
"How do I look in this??" Easy. If she's not already wearing the full ensemble, request her to do so. Then engage in the positives about how it goes with the shoes or matches the top. Maybe how it compliments the skirt..?
"Fine" don't cut it.. Positive feedback on finding something she feels comfortable in goes way further than 15 grand!