T.T.
My DD has PDD/NOS (pervasive developmental disorder)/ High functioning Autism, so I know what you mean about speech delays.
We moved our daughter from her crib to a Full size bed when she turned 2 1/2 and put a LONG rail on the side because she is all over the bed. To her it is like her crib but knows not to stand in it and says in it for the most part.
Her crib is like yours but chose not to convert it to the toddler bed because she would stand in it and also she needed more room to flop around because she would fall out.
NOTE: remove the crib all together when you buy a new bed...she will get confused. Found this out the hard way...my DD kept trying to move to her crib.
So my advice...MOVE TO A FULL SIZE BED and add a EXTRA LONG RAIL and leave enough room at the bottom end of the bed for her to get in and out on her own but the rest of the bed is secure. Chose a bed with a Head and Foot board.
Full size bed is better so if she has a sizure she has plenty of room in the bed without hurting herself.