All three are great resorts.
BLT is my favorite due to the interior design (modern appeals to me) and the ability to walk to MK (and monorail). It is the hardest to reserve, and the most expensive usually. The 2BR there is great, and feels like a ton of space (and is). Stayed there a couple of years ago, and will again this December.
WL (stayed at the resort, not the DVC) has always felt like home to me, and I love it. I would consider looking at Club Level with 2 rooms vs. DVC, as you will have the newest furnishings (most DVC looks kinda dated to me, not a fan of bedspreads). WL has the least expensive club level, and the coolest location. For a once in a lifetime trip, worth it if you are paying out of pocket vs. renting points. Boat to MK is fun, but not as express as walking/monorail.
AKL-Kidaini, we stayed here this past Jan (2br dedicated), and it was great. I love animals, but we didn't see as many as we have in the past. We had a car, and drove everywhere (loved this), but the resort did feel a bit out of the way. You get an extra full bath if you book at Kidani vs. Jambo, and the rooms are newer, I believe.
If you mum is mobile (your use of mum made me miss my BFF from HS who lives in AU...and expecting gumnut #2), then any resort will do, if she would have a hard time going up/down steep stairs on a bus, then BLT should be at the top of your list.