Sell them (try TGR Gear Swap) and take your lumps then never go back to that shop again. They are absolutely without a doubt too short so don't ski them as that will further decrease their value Hopefully they have a decent binding and won't be too difficult to unload. They are a great size for a decent woman skier 5' 5" to 5"9 and 125 to 140 lbs.
Regarding the longer skis question- the contact length on twin tips is shorter than 'regular' skis because of the turned up tail. Eg. my 186 Prophets have the same contact length as my 177 Atomics. In other words, with your height and weight your 172s will ski like a 165s ie; twitchy and sink like a stone.
Regarding 179 versus 186 - My wife is 5'5"/105 lbs and loves her 179's but she is an extraordinary skier. How good a skier are you? Do you ski Eastern trees a lot? If you are a solid intermediate by Western standards and don't ski sugerbush trees then 186. More edge and more float. If you already have skinny short skis for ice days then definitely 186.