ROTFLOL. I know many, many, many folks at JPL on both a professional and personal basis, including many of the women in the link below. I can assure you that there are many, many, many engineers there, both male and female, who wear t-shirts. And shorts. And yes, there are female technical folks at JPL who wear spaghetti strap dresses.
The pictures you are seeing from that link are formal portraits, and (with the notable exception of one individual in that link who has always been known for her fashion sense–especially notable because she is very much the exception) not necessarily representative of “dressing professionally”–for ANY gender–at JPL or in similar environments.
Professional dress standards do of course vary from office to office.