Well, she was mid-30s when she was on ST. She worked regularly starting in 1950, but never got a big role. She was in only eight ST episodes, according to IMDB.
According to Trek histography, Whitney was a substance abuser and “sex addict” who couldn’t be counted upon to know her lines and report to the studio on time, so she was fired after the first eight episodes. She had cameos in later Trek movies.