I introduced my pups to stairs when they were young, so I don't have the problem of "set in their ways".
That being said, I chose stairs because they don't take up the amount of room that a ramp does. Mine took to stairs rapidly - like, within minutes. I only had to teach one, then he taught the others. The rise of the stairs is only 6", and the top step (landing) is even with the mattress top, so they only have to step over.
In the past, with other (and larger) dogs, I used a chest at the end of the bed. It was half way to the top, so it was a good intermediary (not to mention useful). But as the dogs got older, they, too quit using it. I noticed - just like you - that getting down was OK ... it was only up.
Then it dawned on me! It takes more muscles, energy, and stress on old joints to make the spring UP. Down is a lot easier. So that may be the problem with your pup, too: it hurts to go UP.
If her knees/hips/muscles hurt her badly enough, a ramp would be easier, but it will take up more floor space in your room. Place it parallel to your footboard. Otherwise, maybe the stairs would work ... she'll just need a little coaxing to learn.
In either event, good luck. Just remember that old dogs CAN learn new tricks
- but sometimes it takes longer. As soon as she figures out she can keep her independence, she'll love the change in her "routine".
Luck and best wishes to you both.