What is inappropriate dress attire for a 48yr old women with adult children?

My fiance's step mom dresses like she is going to the bars trying to get people to notice her. I am 24 and would not even wear the low cut shirts she wears. Her outfits consist of brands from Ambercrombie, Pink Victoria Secrets, Holister, Arden B, and others. Her clothes look like she is going clubbing ect. I do not even wear bathing suits that are string bikinis and one size to small for her double fake d's. Why do you need to put makeup on and heals when we are going to lay out in the sun? I have less respect for her as a parent because what is she showing her 16 year old daughter, to make matters worse she has a 28 year old son. So me and my fiance are disagreeing over this matter because he doesn't see how it should matter what she dresses like. I personally dont think she is setting good examples for her youngest, Its very hard for me to take her serious when she dresses like that. So how can I explain to my fiance how I think it is inappropriate?