J, I feel bad for your mom. But, it's not the MLL attendant's call, it's up to AC's IT system. The TD or CIBC Visa card must be swiped through their reader and then it makes the decision, not the door-keep. True, some staff will let you into the MLL even if your swiped card fails, heck I've been told by friends that they just accompanied their spouse into the lounge on a regular TD Aero Infinite Visa, but this is up to the agent at the lounge. They likely won't be this gracious if the lounge is very busy/full though. The fact that your mom had an onward boarding pass on AC metal (EWR-YYZ) SHOULD have satisfied the requirements for her to gain entry, but for whatever reason, the AC IT system failed to validate the entry.
We've discussed this over the years in the TD thread, though this also applies to the CIBC Aero Visa cards, which has the same once-annual MLL entry benefit. Clipper and I have written about this in the past, and here is a link to one series of discussion in the TD thread (and I would suggest this thread be moved over to that thread):
http://www.flyertalk.com/forum/air-c...l#post26158193
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Meanwhile, at one time my wife and I flew on an economy-Y (Egads!) award, YYZ-YVR. At the MLL we had about 8 different TD/CIBC Aero Visa cards at our disposal. Mine swiped successfully on the first try. My wife had 2 or 3 of her own cards fail to allow her entry. The attendant was nice (and willing) enough to swipe some of my other Visa cards through the reader and one finally worked. It was confusing, but we think her cards failed because they were all linked to HER Aeroplan number. But I had booked her award using MY Aeroplan points, so this didn't pass the requirements test. So it was one of MY own extra cards with MY Aeroplan number attached to it, that granted her to gain entry to the lounge.
On another occasion where none of our TD/CIBC Aero cards would work, I contacted Aeroplan, who asked me to contact TD (or vice versa), but utlimately you need to contact AC. It's THEIR system that needs to tie everything together. There used to be a page with a form that you can fill in online to complain. I can't find it, now under the newer AC website pages. Eventually they began to discuss the issue with me using email at this account:
[email protected]
In the end we were given two International MLL lounge passes as compensation for their failed AC IT systems. Other people have received discount codes or something like a $50 travel credit. Good luck.