I started as an adult ten years ago.  At this point I would say I play "pretty well."  I can contribute very positively to our community orchestra if I practice A LOT.  I got to this point by:
1.  Trying out teachers until I found one who seemed to really know what he was doing and who pushed me hard.

2.  Practicing as much as I could because I loved the sound of the instrument.  And I loved that I could create that sound.  At first thirty minutes was all I could do, but now I have to hold myself back from playing almost all the time.  For me, practice was never something I "had" to do.

3. Listening to the great, and sometimes not so great, cellists.  If there is a cellist playing within a hundred miles of my home I will be at that concert.

4.  Reading about all aspects of music.

5. Trying different intonation experiences on my own.  Play the C scale over and over. 

The one thing I would really criticize about your current teacher is that she isn't having you "perfect" a piece.  You never really know how well or how poorly you are playing until you get a piece up to a level for public performance.  Also there are bowing techniques that can be learned even in Suzuki books.  the bow hold is the key.

Good luck