Crooked bottom teeth. Is there anything I could do to fix it? (Photo)

Absolutely - go get a second opinion.  Thin teeth do not mean you can't move them - they can actually be easier to shift.  However if your bone levels and periodontal (around the teeth/gum) health is poor - orthodontic movement can be contraindicated.  Hope this helps!

I think you should bet a 2nd opinion.  We do cases like this with Invisalign all the time.  Space needs to be created to allow the crowded teeth to move and straighten.  Space can be gained by doing small amount of sanding in between front teeth, back teeth, or both.  Another way to gain space to straighten teeth is to expand or widen the arch.   As the arch widens, the teeth have more room to be aligned to a straight position.   There may be reasons that are not visible in your photo that prompted your orthodontist to say your teeth cannot be straightened because they are too narrow.  A 2nd professional opinion should be worth your while!

Definitely get a second opinion!!Based on the pictures you posted, I would say this can be corrected rather quickly with Invisalign. You may also want to get veneers on your upper teeth to fix some of the damage and chipping.Good luck!