Ok, if that's what's going on - and honestly, seeing her once every couple of months isn't an accurate picture, then her mother needs a HUGE wake up call. The toilet trainging needs to be followed up - why, whether they've trued - you said her grandmother + aunt talk to her - would they have tried? What about CC? If there are other problems there, impacting TT.
Formula... well, giving it additionally to solids is fine I guess, bit odd but nothing too unusual, but no many other solids? Is she on a prescription formula, and is there other issues there maybe? Any chance she's seeing a speech therapist or OT for oral aversion issues??
Why isn't anyone else doing anything for her