There may be help here in the US, what country are you from, your profile doesnt tell us anything,if you want good advice it would be helpful to know more.
There could be all kinds of problems going on. Fetal alcohol syndrome is a diagnosis. However she should also be seen by a speech and language therapist to assess her own speech abilities and her ability to follow language (as you say she appears to forget familiar words, doesn't respond to directions/questions etc). The speech therapist should also assess her working memory, auditory memory, social skills etc. A clinical psychologist should assess her emotional responses and understanding, her cognitive ability, her bonding issues etc.
Depending on what they find she may also need assessment by an Occupational Therapist.
This child may also have difficulties with executive functions (google that to see what they are).
You don't say what country you are in, but these assessments should be happening as standard, especially as she is being fostered/adopted.
I ahve one exactly like her with same issues she is 9 I love her and want the best for her but no one seems to know what to do. I also need help and am ready to throw in the towel
Isn't Fetal Alcohol Syndrome a diagnosis?
I'm not sure where you are, but I would think that if she's in the foster care system, they would be getting a diagnosis and also putting a treatment plan into place with follow-up (meetings to discuss therapy, progress, etc.).