We have a daughter (adopted from a developing country) who struggles greatly with the language and has been here several years. For those that say to learn English as quickly as possible, it is extremely difficult and will be a challenge that she will need to overcome in order to do well here. There are 3 parts to learning the language---speaking/oral language is first, followed by reading, followed by writing. That is the order the language is typically learned. These 3 components, in any efficient manner, will take close to a decade, if not more, to learn, even with an ELL class. I do highly recommend, if she is close to a public library, to possibly seek out ELL services there.
However, in order to get a job, even a low-skilled position, there are other things that come into play. An application has to be filled out, background checks done, I-9s, W-4s, etc. She has to have her paperwork in order showing she is able to work. If she is unable to speak the language, it's highly unlikely she is able to write the language; therefore, may need assistance from you or someone else in filling out an application and acting as an interpreter to help her get through the interview.
Jobs that come to mind:
Dishwasher
Fast food/basic cooking where she prepares food--fries, burgers, etc.
Cleaning
If she wants to go into retail, she will need to learn our money system and need to have the ability to count change.