In 5 years, you've never used fertilizer? Wow... You should use a good bloom-booster fertilizer in the spring, then a more all-purpose fertilizer the rest of the growing season. Use them about 1/2 strength. East is a good exposure. Carnosa takes some time to bloom and needs to mature, even if it comes off of a blooming plant. (I'm assuming it's carnosa as it's the most common, and since you said your sisters was an old plant, I'm betting that's what it is...) Don't toss it out even if it's stubborn for you - I'm sure you can find someone who will take it off your hands and simply love it for being a healthy, attractive plant, even without blooms.

Denise in Omaha

Something to add to the advice that Denise has given is that Hoya carnosa's blooming can also probably be triggered by a drop between day and night temperature, usually a difference of 10 degrees is good to aim for. Allowing the plant to experience cool nights at about 65F should do the trick if you have the light and nutrition right.
I got a large Hoya carnosa the had never bloomed from a local woman and it bloomed not long after I got it. What I did was repot into a 8" pot with potting soil,orchid bark and perlite. I fertilized and placed the plant in bright indirect light from a South window and it soon developed peduncles on the new growth.

Mike

The reason I had not re-potted or fertilized it or trimmed it (it is hanging halfway to the floor!) is because I was told it didn't like to be pampered or fooled with. My sister's has never been re-potted, fertilized or those new shoots never pruned back & it is ... at least 15 years old! Her's is on a wall across from sun-drenched (warm!)south glass patio doors.

Thanks for the suggestions which I will try ... at least starting with the fertilizer!