Android Device Manager crippled my mom's phone. How do I resolve this?

[D13H4RD2L1V3]

So, long story short.

Was at the airport. Mom went into a slight panic as she thought she had lost her phone. Went to ADM and locked her phone as a precautionary measure as she had sensitive stuff on it. She found it but when I went to unlock it, the password I sent to it didn't work and the phone refused to unlock. Changed it and the earlier one worked but it has since relocked and now would not exit the lockscreen at all.

Tried using my iPad, Moto Z and my laptop to attempt to resolve this, but all of which resulted in failure as each time, ADM keeps saying "Since Google has verified that a screen lock is already set, the password you entered won't be needed."

I don't want to resort to a factory reset as sensitive stuff is stored on it and it being my mom's phone, I'm not sure if she has done any backups recently (and I will be royally hosed if I do resort to the reset).

Suggestions?

Her phone is a ZE551ML variant of the Zenfone 2, BTW.

 

[Rukbat]

If none of the passwords, the old one or the new one, unlock the phone when entered on the phone, bring the phone to the carrier and ask for assistance. (Make sure she has a photo ID with her, to be able to prove that it's her phone.)

 

[D13H4RD2L1V3]

Well, bad has got to worse.

I tried doing a cache wipe to see if any progress can be made. Ended up with the phone refusing to boot, requiring a firmware reflash.

 

[Golfdriver97]

Not good as the reflash will wipe the device.

 

[D13H4RD2L1V3]

AANNNDDD the phone's now completely dead.

The moment I plugged it into my laptop to begin reflashing the firmware on it, it just died.

I plugged it into a battery bank but there's no response. Just to test it, I plugged it into an old Galaxy S3 and that thing charged up.

My luck with phones has been utterly horrendous. From 2 dead LG G4s to a Note 7 that subsequently got recalled to my mom's Zenfone now being dead in my hands. I just hope my Moto Z isn't the next one in line.