17 days post Smart Lipo on arms. Do I have swelling above elbow or is it still fat?

Arms can develop a large degree of swelling if compression garments are not properly worn or not tight enough. Double check with your surgeon to see if you have a hematoma. If they were smaller after lipo, it's probably fluid. Fat doesn't magically grow back. Go for massages as well.

After a Smart Lipo procedure, it’s common
for swelling to last for several weeks to a few months. What you’re
experiencing should dissipate over time, and the best thing you can do to aid
in the healing process is to continue wearing your compression garment as
directed by your surgeon, as well as keeping your sodium intake low. It’s
common for swelling to occur in the lowest part of the treated area, which for
you lands at the elbows. This may explain the current size and tenderness of
that location. If you continue to be concerned or uncomfortable, it’s important
that you follow up with your surgeon.

Despite not having photos, what you are describing is very common when it comes to SmartLipo of the arms. At first, you noticed that the arms were smaller, including the area above the elbow. After two weeks, swelling or edema of the skin and soft tissues settled to the lowest part of the treated area which lies just above the elbows. This is because gravity will tend to draw the swelling to the most dependent portion of the operated areas. Luckily, the fat that has been removed with the operation is gone permanently and the swelling that is temporarily taking up the space above the elbow will dissipate in a few weeks to months to allow the slimming result to show. Wearing the compression garment is helpful; just make sure it starts at the wrist because it will cause swelling just beyond the cuff.