My wife whose been here with me in the UK for 5 years and has ILR wants her mother to visit.

My mother in law speaks no English and has no income and lives with a friend in her house so owns no property.

I am not even sure she has a bank account, looking at the forms it would appear that I can write supporting documentation saying she can stay our home and I can support her. How hard is it when the applicant who will be in her 70's hasn't even a button to her name so to speak?

Any advice gratefully appreciated.

Steve

There's no reason why your MIL shouldn't visit you and your wife, with you providing financial support, but the most difficult part is convincing the Entry Clearance Officer that she will return home at the conclusion of the visit.

The ECO may assume that she wants to join you guys in the UK, she needs to convince them otherwise and that she has ties in Thailand and they are strong enough, I assume at 70 she wont work, does she have any other family?

Yes her other daughter lives there with her own house husband and 2 children..owns home,car and got a good job in local government. I suppose a similar supporting letter from her saying she supports her etc...would help

It wouldn't hurt. Also her other daughter should supply evidence, if she has it, of that support; e.g. monies regularly paid to her mother.