there's other great places to go. Laos,Cambodia, Vietnam.
you can get a free entry into Vietnam if you from UK or other European countries ,there's a place there you could live for 20dollars a day , including a very good hotel . then just pop back for free 30 day visa .could push your luck and ask for a longer visa??
Don't worry. Request a wheelchair at the beginning of her journey, and there will be a wheelchair waiting in Bangkok, she will be taken through immigration V.I.P
(otherwise it would be a long walk to immigration. )