Is a TM30 required for extending my mom's stay in Bangkok after 50 days?

I assume you have a contract with your landlord.

You can just take the contract with you to immigration and say your mum is staying with you and do the extension at the same time.

She might get the fine for not registering straight away or could just say she was staying somewhere else in another province.

All this nonsense that other people are saying about landlords registering you is just that nonsense if you have a contract you just register yourself or your mum in this case.

I don’t even know who my landlord is 🤷🏼‍♂️ I just take my contract to immigration myself.

You could try forcing your landlord to file a TM30 by explaining how you have to report him to Immigration and the Revenue office. But he might just spit the dummy, so a hotel would probably be easier.

You can do the TM30 online yourself, or just ask your landlord to do one now. Either will be accepted.

Ask your landlord to resister her. Date on TM.30 date doesn’t matter as it can be submitted as many times as you need/want. Many people do just to get the receipt when they lose it.

It sounds like you will need to book a hotel, so make sure before you check in that the hotel actually registers TM30's and can provide you with a copy.

IF she entered Thailand as a Visa Exempt Entry...to obtain the 30 day extension of stay, she needs to go to the IT Square in Laksi Plaza in Bangkok

Did she enter Thailand Visa as a VISA EXEMPT ENTRY?

Or with a SETV single entry tourist visa she purchased when she was in the USA?

Have you tried to file a TM30 address registration online?

Yes. The TM30 is required. Have her check into a hotel for a couple of days and apply