No surprises, You wont get a LF Led, as that is the 125kHz freq.
NFC is your HF 13.56MHz.
I guess your are talking about your RFID Diagnostic Card
Do you have an X Field Detector ( 13.56 )
This is really useful for finding the optimal position and orientation of your phones antenna?
This can vary widely from phone to phone but generally a square or rectangular shape.
See of you can find an image online of your / wifes phone NFC antenna position.
If you dont have a x Field detector, you can still use your diagnostic card, as the phone will pulse the signal strength will change ( My phone pulses all along the perimeter 5 x weak 1 x Strong ) use your diagnostic card to find the strongest ( Brightest ) area and remember to move slowly. When you can visualize the antenna location, place you device against your antenna in opposing orientation ( – | ) to find the optimal location for a good read.
Indeed the case may be the problem especially if is, quite thick, made of metal or a combination of both like mine with a Mophie battery pack case.
Again, sorry if you have already tried these things
Looks Like @turbo2ltr beat me to it, also his video is better than my ramblings