Can my wife do the TM30 online after we return to Thailand?

You might consider trying to make the account prior to arrival depending on the situation of the address/owner. When we created an account for my girlfriends place, it did take a while to get it organized. If one needs to file within 24 hours, it might be difficult to do it if there was trouble getting the account created quickly. Now that we have the account for her place, and i have the log in info, i did the TM30 notification myself.

I just do it for my wife. I created an account using her name and info, and file the TM30 as necessary. This saves her having to deal with the website and stuff.

She can make an account at this link,

she adds an address,

she can file a TM30 on someone at that address,

save it

and

she then searches for the data she just saved so she can print out the PDF file that is the TM30

Have her read the user guide